Solid state electrolyte for lithium secondary battery

ABSTRACT

Provided is a solid state electrolyte composition for a rechargeable lithium battery. The electrolyte composition comprises a lithium ion-conducting polymer matrix or binder and lithium ion-conducting inorganic species that is dispersed in or chemically bonded by the polymer matrix or binder, wherein the lithium ion-conducting inorganic species is selected from Li 2 CO 3 , Li 2 O, Li 2 C 2 O 4 , LiOH, LiX, ROCO 2 Li, HCOLi, ROLi, (ROCO 2 Li) 2 , (CH 2 OCO 2 Li) 2 , Li 2 S, Li x SO y , or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, x=0-1, y=1-4; and wherein the polymer matrix or binder is in an amount from 1% to 99% by volume of the electrolyte composition. Also provided are a process for producing this solid state electrolyte and a lithium secondary battery containing such a solid state electrolyte.

FIELD OF THE INVENTION

The present invention provides a solid state electrolyte for alithium-ion battery or a rechargeable lithium metal battery (havinglithium metal as the anode active material).

BACKGROUND

Rechargeable lithium-ion (Li-ion), lithium metal, lithium-sulfur, and Limetal-air batteries are considered promising power sources for electricvehicle (EV), hybrid electric vehicle (HEV), and portable electronicdevices, such as lap-top computers and mobile phones. Lithium as a metalelement has the highest lithium storage capacity (3,861 mAh/g) comparedto any other metal or metal-intercalated compound as an anode activematerial (except Li_(4.4)Si, which has a specific capacity of 4,200mAh/g). Hence, in general, Li metal batteries (having a lithium metalanode) have a significantly higher energy density than lithium-ionbatteries (having a graphite anode).

Historically, rechargeable lithium metal batteries were produced usingnon-lithiated compounds having relatively high specific capacities, suchas TiS₂, MoS₂, MnO₂, CoO₂, and V₂O₅, as the cathode active materials,which were coupled with a lithium metal anode. When the battery wasdischarged, lithium ions were transferred from the lithium metal anodeto the cathode through the electrolyte and the cathode became lithiated.Unfortunately, upon repeated charges and discharges, the lithium metalresulted in the formation of dendrites at the anode that ultimatelycaused internal shorting, thermal runaway, and explosion. As a result ofa series of accidents associated with this problem, the production ofthese types of secondary batteries was stopped in the early 1990'sgiving ways to lithium-ion batteries.

Even now, cycling stability and safety concerns remain the primaryfactors preventing the further commercialization of Li metal batteries(e.g. Lithium-sulfur and Lithium-transition metal oxide cells) for EV,HEV, and microelectronic device applications. Again, cycling stabilityand safety issues of lithium metal rechargeable batteries are primarilyrelated to the high tendency for Li metal to form dendrite structuresduring repeated charge-discharge cycles or overcharges, leading tointernal electrical shorting and thermal runaway. This thermal runawayor even explosion is caused by the organic liquid solvents used in theelectrolyte (e.g. carbonate and ether families of solvents), which areunfortunately highly volatile and flammable.

Many attempts have been made to address the dendrite and thermal runawayissues. However, despite these earlier efforts, no rechargeable Li metalbatteries have succeeded in the market place. This is likely due to thenotion that these prior art approaches still have major deficiencies.For instance, in several cases, the anode or electrolyte structuresdesigned for prevention of dendrites are too complex. In others, thematerials are too costly or the processes for making these materials aretoo laborious or difficult. In most of the lithium metal cells andlithium-ion cells, the electrolyte solvents are flammable. An urgentneed exists for a simpler, more cost-effective, and easier to implementapproach to preventing Li metal dendrite-induced internal short circuitand thermal runaway problems in Li metal batteries and otherrechargeable lithium batteries.

Parallel to these efforts and prompted by the aforementioned concernsover the safety of earlier lithium metal secondary batteries led to thedevelopment of lithium-ion secondary batteries, in which pure lithiummetal sheet or film was replaced by carbonaceous materials (e.g. naturalgraphite particles) as the anode active material. The carbonaceousmaterial absorbs lithium (through intercalation of lithium ions or atomsbetween graphene planes, for instance) and desorbs lithium ions duringthe re-charge and discharge phases, respectively, of the lithium-ionbattery operation. The carbonaceous material may comprise primarilygraphite that can be intercalated with lithium and the resultinggraphite intercalation compound may be expressed as Li_(x)C₆, where x istypically less than 1.

Although lithium-ion (Li-ion) batteries are promising energy storagedevices for electric drive vehicles, state-of-the-art Li-ion batterieshave yet to meet the cost, safety, and performance targets. Li-ion cellstypically use a lithium transition-metal oxide or phosphate as apositive electrode (cathode) that de/re-intercalates Li⁺ at a highpotential with respect to the carbon negative electrode (anode). Thespecific capacity of lithium transition-metal oxide or phosphate basedcathode active material is typically in the range of 140-170 mAh/g. As aresult, the specific energy of commercially available Li-ion cells istypically in the range of 120-220 Wh/kg, most typically 150-180 Wh/kg.These specific energy values are two to three times lower than whatwould be required for battery-powered electric vehicles to be widelyaccepted.

Furthermore, the same flammable solvents previously used for lithiummetal secondary batteries are also used in most of the lithium-ionbatteries. Despite the notion that there is significantly reducedpropensity of forming dendrites in a lithium-ion cell (relative to alithium metal cell), the lithium-ion cell has its own intrinsic safetyissue. For instance, the transition metal elements in the lithium metaloxide cathode are highly active catalysts that can promote andaccelerate the decomposition of organic solvents, causing thermalrunaway or explosion initiation to occur at a relatively low electrolytetemperature (e.g. <200° C., as opposed to normally 400° C. without thecatalytic effect).

Ionic liquids (ILs) are a new class of purely ionic, salt-like materialsthat are liquid at unusually low temperatures. The official definitionof ILs uses the boiling point of water as a point of reference: “Ionicliquids are ionic compounds which are liquid below 100° C.”. Aparticularly useful and scientifically interesting class of ILs is theroom temperature ionic liquid (RTIL), which refers to the salts that areliquid at room temperature or below. RTILs are also referred to asorganic liquid salts or organic molten salts. An accepted definition ofan RTIL is any salt that has a melting temperature lower than ambienttemperature.

Although ILs were suggested as a potential electrolyte for rechargeablelithium batteries due to their non-flammability, conventional ionicliquid compositions have not exhibited satisfactory performance whenused as an electrolyte likely due to several inherent drawbacks: (a) ILshave relatively high viscosity at room or lower temperatures; thus beingconsidered as not amenable to lithium ion transport; (b) For Li—S celluses, ILs are capable of dissolving lithium polysulfides at the cathodeand allowing the dissolved species to migrate to the anode (i.e., theshuttle effect remains severe); and (c) For lithium metal secondarycells, most of the ILs strongly react with lithium metal at the anode,continuing to consume Li and deplete the electrolyte itself duringrepeated charges and discharges. These factors lead to relatively poorspecific capacity (particularly under high current or highcharge/discharge rate conditions, hence lower power density), lowspecific energy density, rapid capacity decay and poor cycle life.Furthermore, ILs remain extremely expensive. Consequently, as of today,no commercially available lithium battery makes use of an ionic liquidas the primary electrolyte component.

With the rapid development of hybrid (HEV), plug-in hybrid electricvehicles (HEV), and all-battery electric vehicles (EV), there is anurgent need for anode and cathode materials and electrolytes thatprovide a rechargeable battery with a significantly higher specificenergy, higher energy density, higher rate capability, long cycle life,and safety. One of the most promising energy storage devices is thelithium-sulfur (Li—S) cell since the theoretical capacity of Li is 3,861mAh/g and that of S is 1,675 mAh/g. In its simplest form, a Li—S cellconsists of elemental sulfur as the positive electrode and lithium asthe negative electrode. The lithium-sulfur cell operates with a redoxcouple, described by the reaction S₈+16Li

8Li₂S that lies near 2.2 V with respect to Li⁺/Li^(o). Thiselectrochemical potential is approximately ⅔ of that exhibited byconventional positive electrodes. However, this shortcoming is offset bythe very high theoretical capacities of both Li and S. Thus, comparedwith conventional intercalation-based Li-ion batteries, Li—S cells havethe opportunity to provide a significantly higher energy density (aproduct of capacity and voltage). Values can approach 2,500 Wh/kg or2,800 Wh/l based on the combined Li and S weight or volume (not based onthe total cell weight or volume), respectively, assuming completereaction to Li₂S. With a proper cell design, a cell-level specificenergy of 1,200 Wh/kg (of cell weight) and cell-level energy density of1,400 Wh/l (of cell volume) should be achievable. However, the currentLi-sulfur experimental cells of industry leaders in sulfur cathodetechnology have a maximum cell specific energy of 250-400 Wh/kg (basedon the total cell weight), far less than what could be obtained in realpractice.

In summary, despite its considerable advantages, the rechargeablelithium metal cell in general and the Li—S cell and the Li-air cell inparticular are plagued with several major technical problems that havehindered its widespread commercialization:

-   (1) Conventional lithium metal secondary cells (e.g., rechargeable    Li metal cells, Li—S cells, and Li-Air cells) still have dendrite    formation and related internal shorting and thermal runaway issues.    Also, conventional Li-ion cells still make use of significant    amounts of flammable liquids (e.g. propylene carbonate, ethylene    carbonate, 1,3-dioxolane, etc.) as the primary electrolyte solvent,    risking danger of explosion;-   (2) The Li—S cell tends to exhibit significant capacity degradation    during discharge—charge cycling. This is mainly due to the high    solubility of the lithium polysulfide anions formed as reaction    intermediates during both discharge and charge processes in the    polar organic solvents used in electrolytes. During cycling, the    lithium polysulfide anions can migrate through the separator and    electrolyte to the Li negative electrode whereupon they are reduced    to solid precipitates (Li₂S₂ and/or Li₂S), causing active mass loss.    In addition, the solid product that precipitates on the surface of    the positive electrode during discharge can become electrochemically    irreversible, which also contributes to active mass loss.-   (3) More generally speaking, a significant drawback with cells    containing cathodes comprising elemental sulfur, organosulfur and    carbon-sulfur materials relates to the dissolution and excessive    out-diffusion of soluble sulfides, polysulfides, organo-sulfides,    carbon-sulfides and/or carbon-polysulfides (hereinafter referred to    as anionic reduction products) from the cathode into the rest of the    cell. This phenomenon is commonly referred to as the Shuttle Effect.    This process leads to several problems: high self-discharge rates,    loss of cathode capacity, corrosion of current collectors and    electrical leads leading to loss of electrical contact to active    cell components, fouling of the anode surface giving rise to    malfunction of the anode, and clogging of the pores in the cell    membrane separator which leads to loss of ion transport and large    increases in internal resistance in the cell.

In response to these challenges, new electrolytes, protective films forthe lithium anode, and solid electrolytes have been developed. Someinteresting cathode developments have been reported recently to containlithium polysulfides; but, their performance still fall short of what isrequired for practical applications. Despite the various approachesproposed for the fabrication of high energy density rechargeable cellscontaining elemental sulfur, organo-sulfur and carbon-sulfur cathodematerials, or derivatives and combinations thereof, there remains a needfor materials and cell designs that (a) retard the out-diffusion ofanionic reduction products, from the cathode compartments into othercomponents in these cells, (b) improve the battery safety, and (c)provide rechargeable cells with high capacities over a large number ofcycles.

Although solid electrolytes are effective in addressing the lithiummetal dendrite and flammability issues, conventional solid-stateelectrolytes have the following major deficiencies: low lithium ionconductivities (typically <<10⁻⁴ S/cm, and mostly <<10⁻⁵ S/cm),difficulty in making solid-state electrolyte (high temperature sinteringtypically required) and implementing it in a battery cell, extremebrittleness, no flexibility (hence, not being compliant and being inpoor ionic contact with the anode and/or cathode and, hence, poor activematerial utilization efficiency), and high costs.

Hence, a general object of the present invention is to provide anelectrolyte system for a rechargeable lithium cell that exhibits a highenergy density, high power density, long cycle life, and no danger ofexplosion due to the use of a safer, non-flammable, solid stateelectrolyte. This solid state electrolyte overcomes the aforementioneddeficiencies.

The invention also provides a rechargeable lithium cell containing sucha safe electrolyte system. This lithium cell includes the lithium metalsecondary cell (e.g. Li—S, Li—TiS₂, Li—Se, Li—MoS₂, Li—VO₂, and Li-air,just to name a few), lithium-ion cell (e.g. graphite-LiMn₂O₄,Si—Li_(x)Ni_(y)Mn_(z)O₂, etc.), Li-ion sulfur cell (e.g. prelithiatedSi—S cell), and hybrid lithium cell (wherein at least one electrodeoperates on lithium insertion or intercalation).

A specific object of the present invention is to provide a rechargeableLi—S battery that exhibits an exceptionally high specific energy or highenergy density and a high level of safety. One specific technical goalof the present invention is to provide a safe Li metal-sulfur or Liion-sulfur cell having a long cycle life and a cell specific energygreater than 400 Wh/Kg, preferably greater than 500 Wh/Kg, and morepreferably greater than 600 Wh/Kg (all based on the total cell weight).

Another specific object of the present invention is to provide a safelithium-sulfur cell that exhibits a high specific capacity (higher than1,200 mAh/g based on the sulfur weight, or higher than 1,000 mAh/g basedon the cathode composite weight, including sulfur, conducting additiveand conductive substrate, and binder weights combined, but excluding theweight of cathode current collector). The specific capacity ispreferably higher than 1,400 mAh/g based on the sulfur weight alone orhigher than 1,200 mAh/g based on the cathode composite weight. This mustbe accompanied by a high specific energy, good resistance to dendriteformation, good resistance to thermal runaway, no possibility of anexplosion, and a long and stable cycle life.

It may be noted that in most of the open literature reports (scientificpapers) on Li—S cells, scientists choose to express the cathode specificcapacity based on the sulfur weight or lithium polysulfide weight alone(not on the total cathode composite weight), but unfortunately a largeproportion of non-active materials (those not capable of storinglithium, such as conductive additive and binder) is typically used intheir Li—S cells. Similarly, for lithium-vanadium oxide cells,scientists also tend to report the cathode specific capacity based onthe vanadium oxide weight only. For practical usage purposes, it is moremeaningful to use the cathode composite weight-based capacity value.

A specific object of the present invention is to provide a rechargeablelithium-sulfur cell based on rational materials and battery designs thatovercome or significantly reduce the following issues commonlyassociated with conventional Li—S cells: (a) dendrite formation(internal shorting); (b) extremely low electric and ionic conductivitiesof sulfur, requiring large proportion (typically 30-55%) of non-activeconductive fillers and having significant proportion of non-accessibleor non-reachable sulfur or lithium polysulfides); (c) dissolution oflithium polysulfide in electrolyte and migration of dissolved lithiumpolysulfides from the cathode to the anode (which irreversibly reactwith lithium at the anode), resulting in active material loss andcapacity decay (the shuttle effect); and (d) short cycle life.

A very important object of the present invention is to provide a simple,cost-effective, and easy-to-implement approach to preventing potentialLi metal dendrite-induced internal short circuit and thermal runawayproblems in various Li metal and Li-ion batteries.

SUMMARY OF THE INVENTION

The present invention provides a solid state electrolyte composition fora rechargeable lithium battery. This electrolyte composition comprises alithium ion-conducting polymer matrix or binder and lithiumion-conducting inorganic species that is dispersed in or chemicallybonded by the polymer matrix or binder, wherein the lithiumion-conducting inorganic species is selected from Li₂CO₃, Li₂O, Li₂C₂O₄,LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S,Li_(x)SO_(y), or a combination thereof, wherein X=F, Cl, I, or Br, R=ahydrocarbon group, x=0-1, y=1-4; and wherein the polymer matrix orbinder is in an amount from 1% to 99% by volume of the electrolytecomposition (preferably from 5% to 95% and more preferably from 20% to80%).

The invention also provides a lithium secondary battery containing ananode, a cathode, and the presently invented solid state electrolyte.The lithium secondary battery can be a lithium-ion battery, arechargeable lithium metal battery, a lithium-sulfur battery, alithium-selenium battery, or a lithium-air battery.

In certain embodiments, the polymer matrix or binder comprises asulfonated polymer, a mixture of a sulfonated polymer and anelectron-conducting polymer (intended primarily for use in the cathodeside where the cathode active materials are typically low in electronicconductivity), a mixture of a sulfonated polymer and an electronicallynon-conducting polymer, or a mixture of an electron-conducting polymerand a lithium ion-conducting polymer. In an embodiment, the polymermatrix or binder is selected from sulfonated polyaniline, sulfonatedpolypyrrole, sulfonated polythiophene, sulfonated polyfuran, or acombination thereof.

The sulfonated polymer may be selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene, sulfonated perfluoroethylene-propylenecopolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer,sulfonated polyvinylidene fluoride, sulfonated copolymers ofpolyvinylidene fluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof.

In certain embodiments, the polymer matrix or binder comprises a mixtureof an electron-conducting polymer and a lithium ion-conducting polymer,wherein the lithium ion-conducting polymer is selected from the groupconsisting of poly(perfluoro sulfonic acid), sulfonatedpolytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives ofpolytetra-fluoroethylene, sulfonated polysulfone, sulfonated poly(etherketone), sulfonated poly (ether ether ketone), sulfonated polystyrene,sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated poly chloro-trifluoroethylene, sulfonatedperfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, sulfonated copolymers ofethylene and tetrafluoroethylene, polybenzimidazole, and chemicalderivatives, copolymers, and blends thereof, wherein theelectron-conducting polymer-to-lithium ion-conducting polymer weightratio is from 1/99 to 99/1. The electron-conducting polymer is selectedfrom the group consisting of polyaniline, polypyrrole, polythiophene,polyfuran, bi-cyclic polymers, derivatives thereof, and combinationsthereof.

In certain embodiments, the polymer matrix or binder contains a lithiumion-conducting polymer selected from poly(ethylene oxide) (PEO),Polypropylene oxide, poly(acrylonitrile) (PAN), poly(methylmethacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), aderivative thereof, or a combination thereof.

The present invention also provides an alternative solid stateelectrolyte composition for a rechargeable lithium battery. Thiselectrolyte composition comprises a lithium ion-conducting polymermatrix or binder selected specifically from a sulfonated polymer and alithium ion-conducting inorganic species that is dispersed in orchemically bonded by the polymer matrix or binder. The lithiumion-conducting inorganic species contains a lithium salt selected fromlithium perchlorate, LiClO₄, lithium hexafluorophosphate, LiPF₆, lithiumborofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆, lithiumtrifluoro-metasulfonate, LiCF₃SO₃, bis-trifluoromethyl sulfonylimidelithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB, lithiumoxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof; and wherein the polymer matrixor binder is in an amount from 1% to 99% by volume of the electrolytecomposition (preferably from 5% to 95% and more preferably from 20% to80%). In this embodiment, the sulfonated polymer is preferably selectedfrom sulfonated polytetrafluoroethylene, sulfonated perfluoroalkoxyderivatives of polytetra-fluoroethylene, sulfonated polysulfone,sulfonated poly(ether ketone), sulfonated poly (ether ether ketone),sulfonated polystyrene, sulfonated polyimide, sulfonatedstyrene-butadiene copolymers, sulfonated poly chloro-trifluoroethylene,sulfonated perfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, poly(perfluoro sulfonicacid), sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof.

The lithium ion-conducting polymer matrix may further contain particlesof a filler dispersed therein. The filler may be selected from a metaloxide, metal carbide, metal nitride, metal boride, metal dichalcogenide,or a combination thereof. Preferably, the filler is selected from anoxide, dichalcogenide, trichalcogenide, sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, vanadium, chromium, cobalt, manganese, iron, or nickel in ananowire, nano-disc, nano-ribbon, or nano platelet form.

The filler may be selected from nano discs, nano platelets, or nanosheets of an inorganic material selected from: (a) bismuth selenide orbismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof; wherein the discs, platelets, or sheets havea thickness less than 100 nm. The filler, if present, contains defectsto promote migration of lithium or sodium ions. Preferably the filler isfrom 1% to 30% by volume.

Preferably and typically, the lithium ion-conducting inorganic specieshas a room temperature ion conductivity no less than 10⁻⁴ S/cm, morepreferably no less than 10⁻³ S/cm.

It may be noted that lithium ion-conducting species (e.g. Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, and Li_(x)SO_(y)) are available from commercial sources, thesespecies, individually or separately, can be readily preparedelectrochemically (e.g. preferably in the presence of a lithiumion-conducting polymer).

Also provided is an alternative solid state electrolyte composition fora rechargeable lithium battery. This electrolyte composition comprises alithium ion-conducting polymer matrix or binder selected from asulfonated polymer and a lithium ion-conducting inorganic species thatis dispersed in or chemically bonded by the polymer matrix or binder.The lithium ion-conducting inorganic species contains a lithium saltthat is commonly used in a liquid electrolyte for lithium-ion batteries.However, no liquid solvent is utilized herein to make an electrolyte;instead, a sulfonated polymer is used. The lithium salt is preferablyselected from lithium perchlorate, LiClO₄, lithium hexafluorophosphate,LiPF₆, lithium borofluoride, LiBF₄, lithium hexafluoroarsenide, LiAsF₆,lithium trifluoro-metasulfonate, LiCF₃SO₃, bis-trifluoromethylsulfonylimide lithium, LiN(CF₃SO₂)₂, lithium bis(oxalato)borate, LiBOB,lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium nitrate, LiNO₃, Li-Fluoroalkyl-Phosphates,LiPF₃(CF₂CF₃)₃, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof; and wherein the polymer matrixor binder is in an amount from 1% to 99% by volume of the electrolytecomposition (preferably from 5% to 95% and more preferably from 20% to80%).

In this alternative embodiment, the sulfonated polymer is preferablyselected from sulfonated polytetrafluoroethylene, sulfonatedperfluoroalkoxy derivatives of polytetra-fluoroethylene, sulfonatedpolysulfone, sulfonated poly(ether ketone), sulfonated poly (ether etherketone), sulfonated polystyrene, sulfonated polyimide, sulfonatedstyrene-butadiene copolymers, sulfonated poly chloro-trifluoroethylene,sulfonated perfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, poly(perfluoro sulfonicacid), sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof.

The present invention also provides a unique process for producing thesolid state electrolyte composition that contains the lithium-containinginorganic species (i.e. Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li,HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, and Li_(x)SO_(y)). Theseinorganic species are produced by electrochemical decomposition of theconventional liquid electrolytes (lithium salt+organic solvent) on anelectrochemical electrode. In some preferred embodiments, the processcomprises (a) preparing a working electrode containing a conductivematerial (e.g. a lithium ion-conducting polymer and/or a carbonmaterials such as an amorphous carbon or polymeric carbon matrix); (b)preparing a counter electrode containing lithium metal or alloy; (c)bringing the working electrode and the counter electrode in contact withan electrolyte containing a solvent and a lithium salt dissolved in thesolvent; and (d) applying a current or voltage to the working electrodeand the counter electrode to induce an electrochemical oxidativedecomposition and/or a reductive decomposition of the electrolyte and/orthe salt for forming the lithium-containing inorganic species to producelithium ion-conducting inorganic species (Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH,LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y),or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbongroup, x=0-1, y=1-4) that are chemically bonded to conductive materialsurfaces. The process can further contain combining the lithiumion-conducting inorganic species (with or without the carbon material)with a lithium ion-conducting polymer to form the solid stateelectrolyte composition.

In this process, there is a broad array of lithium salts and solvents tochoose from to provide, or electrochemically produce therefrom, a widevariety of lithium-conducting species or mixtures. For instance, thelithium salt may be selected from lithium perchlorate, LiClO₄, lithiumhexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄, lithiumhexafluoroarsenide, LiAsF₆, lithium trifluoro-metasulfonate, LiCF₃SO₃,bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂, lithiumbis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate, LiBF₂C₂O₄,lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate, LiNO₃,Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide, LiBETI, lithium bis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide, lithiumtrifluoro methanesulfonimide, LiTFSI, an ionic liquid-based lithiumsalt, or a combination thereof. The solvent may be selected from1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycoldimethylether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME),diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE),sulfone, sulfolane, ethylene carbonate (EC), dimethyl carbonate (DMC),methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate,methyl propionate, propylene carbonate (PC), gamma-butyrolactone (γ-BL),acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methylformate (MF), toluene, xylene, methyl acetate (MA), fluoroethylenecarbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), ahydrofluoroether, an ionic liquid solvent, or a combination thereof.

Preferably, the process is a roll-to-roll process that includespreparing the working electrode in a roll form supported by a feederroller, and the step of bringing the working electrode and the counterelectrode in contact with the electrolyte contains unwinding the workingelectrode from the feeder roller, and feeding the working electrode intothe electrolyte.

Also provided is another process for producing the solid stateelectrolyte composition. The process comprises (a) preparing a workingelectrode containing a lithium ion-conducting polymer; (b) preparing acounter electrode containing lithium metal or alloy; (c) bringing theworking electrode and the counter electrode in physical contact witheach other and in contact with an electrolyte containing a solvent and alithium salt or sodium salt dissolved in the solvent; wherein theworking electrode and the counter electrode are brought to be at thesame electrochemical potential level, inducing a chemical reactionbetween the lithium metal or alloy and the lithium ion-conductingpolymer and inducing electrochemical decomposition of the electrolytefor forming the lithium-containing inorganic species that are attachedor chemically bonded to the lithium ion-conducting polymer to form thesolid state electrolyte composition.

Alternatively, the process comprises (a) preparing a working electrodecontaining a carbon material; (b) preparing a counter electrodecontaining lithium metal or alloy; (c) bringing the working electrodeand the counter electrode in physical contact with each other and incontact with an electrolyte containing a solvent and a lithium saltdissolved in the solvent; wherein the working electrode and the counterelectrode are brought to be at the same electrochemical potential level,inducing a chemical reaction between the lithium metal or alloy and thecarbon material and inducing electrochemical decomposition of theelectrolyte for forming the lithium-containing inorganic species onsurfaces of the carbon material; and (d) mixing the lithium-containinginorganic species, with or without the carbon material, with a lithiumion-conducting polymer for forming the solid state electrolytecomposition. The lithium-containing inorganic species may be removed orseparated from the surfaces of the carbon material prior to mixing witha lithium ion-conducting polymer. The process is preferably conducted ina roll-to-roll manner. The carbon material may be selected from anamorphous carbon, polymeric carbon (carbonized resin), activated carbon,carbon black, graphite particles, graphene sheets, carbon nanotubes,carbon fibers, graphite fibers, carbon nano-fibers, or a combinationthereof.

The invention also provides a process for producing the solid stateelectrolyte composition using a direct internal shorting method. Theprocess comprises: (a) preparing a working electrode containing aconductive material (e.g. preferably an amorphous carbon or polymericcarbon matrix and an optional carbon or graphite reinforcement phase);(b) preparing a counter electrode containing lithium metal or alloy; and(c) bringing the working electrode and the counter electrode in physicalcontact with each other and in contact with an electrolyte containing asolvent and a lithium salt dissolved in the solvent; wherein the workingelectrode and the counter electrode are brought to be at the sameelectrochemical potential level, inducing a chemical reaction betweenthe lithium metal or alloy and the conductive material and inducingelectrochemical decomposition of the electrolyte for forming the desiredlithium-containing species that are attached to the conductive material(e.g. bonded to the amorphous carbon or polymeric carbon matrix and/orthe optional carbon or graphite reinforcement phase). Thelithium-containing species are then removed or separated from theconductive material and then mixed with a lithium ion-conducting polymerto produce the solid electrolyte composition. Alternatively, theconductive material in the working electrode may contain a lithiumion-conducting polymer, allowing the lithium-containing species todeposit thereon.

The advantages and features of the present invention will become moretransparent with the description of the following best mode practice andillustrative examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Schematic of a rechargeable lithium metal battery.

FIG. 2 An electrochemical energy diagram to illustrate electrochemicalpotential or energetic conditions under which electrolyte in anelectrochemical reactor undergoes oxidative or reductive degradation atthe electrode-electrolyte boundary.

FIG. 3 Lithium ion conductivity values plotted as a function oflithium-containing inorganic species percentage in a sulfonatedpolyaniline matrix.

FIG. 4 Lithium ion conductivity values in a solid polymer mixture of asulfonated polymer (S-PEEK or S-PTFE) and a conventional electrolytepolymer (PEO or PPO) plotted as a function of the sulfonated polymerproportion (each containing 30% by weight of lithium salt).

FIG. 5 The Ragone plots (power density vs. energy density) of threecells tested in different discharge rates (different current densities).The 3 different electrolytes in these 3 cells are the presently inventedsolid electrolyte (C5 in Table 2), liquid electrolyte (1 M of LiPF₆ inPC-EC solvent mixture), and a prior art PEO-LiPF₆ polymer electrolyte.

FIG. 6 The capacity retention of 2 lithium-ion cells (one with aninventive solid state electrolyte and the other with a PEO-based solidpolymer electrolyte) plotted as a function of discharge C rates.

FIG. 7 The Ragone plots (power density vs. energy density) of three Li—Scells: first one with the inventive solid state electrolyte, second withliquid electrolyte, and third with conventional polymer solidelectrolyte.

FIG. 8 The specific discharge capacities of two Li—S cells, onecontaining the presently invented solid state electrolyte and the otherliquid electrolyte, are plotted as a function of the number ofcharge/discharge cycles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a safe and high-performing solid stateelectrolyte for a rechargeable lithium battery, which can be any ofvarious types of lithium-ion cells or lithium metal cells (e.g. Li-metaloxide, Li—S, Li-air, and Li—Se cells, etc.). A high degree of safety isimparted to this battery by a novel and unique solid-state electrolytethat is essentially non-flammable and would not initiate a fire and,hence, would not pose explosion danger. This invention has solved thevery most critical issue that has plagued the lithium-metal andlithium-ion industries for more than two decades.

For illustration purpose, the following discussion of preferredembodiments is primarily based on Li—S cells (as an example), but thesame or similar principles and procedures are applicable to all otherrechargeable lithium metal batteries (using lithium metal or metal alloyas the anode active material). The cathode active materials can be, forinstance, a transition metal oxide (e.g. V₂O₅) or sulfide (e.g. MoS₂),sulfur or polysulfide (e.g. lithium polysulfide), or just outside air(for a lithium-air). The solid state electrolyte can also be used inlithium-ion cells.

This electrolyte composition comprises a lithium ion-conducting polymermatrix or binder and lithium ion-conducting inorganic species (alsoreferred to as lithium-containing inorganic species) that is dispersedin or chemically bonded by the polymer matrix or binder. The lithiumion-conducting inorganic species is selected from Li₂CO₃, Li₂O, Li₂C₂O₄,LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S,Li_(x)SO_(y), or a combination thereof, wherein X=F, Cl, I, or Br, R=ahydrocarbon group, x=0-1, y=1-4. The polymer matrix or binder is in anamount from 1% to 99% by volume of the electrolyte composition.

We have surprisingly observed that a wide variety of sulfonated polymersare highly conducting to lithium ions, particularly when being used incombination with the aforementioned lithium ion-conducting inorganicspecies to form a composite solid electrolyte. The polymer matrix orbinder may be selected from a sulfonated polymer itself, a mixture of asulfonated polymer and an electron-conducting polymer (intendedprimarily for use in the cathode side), a mixture of a sulfonatedpolymer and an electronically non-conducting polymer, or a mixture of anelectron-conducting polymer and a lithium ion-conducting polymer.

In an embodiment, the polymer matrix or binder is selected fromsulfonated polyaniline, sulfonated polypyrrole, sulfonatedpolythiophene, sulfonated polyfuran, or a combination thereof. Such apolymer is not only lithium ion-conducting but also electron-conductingand, hence, cannot be used as the sole electrolyte without another layerof non-electron-conducting electrolyte or a porous separator layer.However, it is highly advantageous to implement such a polymerelectrolyte in the cathode of a Li—S or Li—Se battery to reducedissolution of sulfur, lithium polysulfide, selenium, or lithiumselenide (for reduced or eliminated shuttle effect) and to increase theelectrical conductivity of the cathode layer (for enhanced cathodeactive material utilization efficiency).

The sulfonated polymer may be selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene, sulfonated perfluoroethylene-propylenecopolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer,sulfonated polyvinylidene fluoride, sulfonated copolymers ofpolyvinylidene fluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof.

These sulfonated polymers can be easily mixed with the aforementionedlithium ion-conducting inorganic species (e.g. Li₂CO₃, Li₂O, Li₂C₂O₄,LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S,Li_(x)SO_(y), and their mixtures via any solution mixing or melt mixingmethod well-known in the art. These inorganic species are commerciallyavailable or readily synthesizable in the laboratory. However, later on,we shall introduce a new approach that entails in situ formation ofthese lithium ion-conducting inorganic species (also referred to aslithium-containing inorganic species) on surfaces of various sulfonatedpolymers and their blends.

In certain embodiments, the polymer matrix or binder comprises a mixtureof an electron-conducting polymer and a lithium ion-conducting polymer,wherein the lithium ion-conducting polymer is selected from the groupconsisting of poly(perfluoro sulfonic acid), sulfonatedpolytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives ofpolytetra-fluoroethylene, sulfonated polysulfone, sulfonated poly(etherketone), sulfonated poly (ether ether ketone), sulfonated polystyrene,sulfonated polyimide, sulfonated styrene-butadiene copolymers,sulfonated poly chloro-trifluoroethylene, sulfonatedperfluoroethylene-propylene copolymer, sulfonatedethylene-chlorotrifluoroethylene copolymer, sulfonatedpolyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoridewith hexafluoropropene and tetrafluoroethylene, sulfonated copolymers ofethylene and tetrafluoroethylene, polybenzimidazole, and chemicalderivatives, copolymers, and blends thereof, wherein theelectron-conducting polymer-to-lithium ion-conducting polymer weightratio is from 1/99 to 99/1. The electron-conducting polymer is selectedfrom the group consisting of polyaniline, polypyrrole, polythiophene,polyfuran, bi-cyclic polymers, derivatives thereof, and combinationsthereof. Such a mixture can be a good lithium ion-conductor, but poorelectron conductor provided the electron-conducting polymer component ofthe mixture is less than 30% by volume. The mixture would be a very goodelectron-conductor if the electron-conducting polymer component of themixture exceeds 70%.

In certain desirable embodiments, the polymer matrix or binder containsa lithium ion-conducting polymer selected from poly(ethylene oxide)(PEO), Polypropylene oxide, poly(acrylonitrile) (PAN), poly(methylmethacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), aderivative thereof, or a combination thereof.

The presently invented solid-state electrolyte is not only dendritepenetration resistant but also highly lithium ion-conducting with theconductivity typically >>10⁻⁵ S/cm, more typically >>10⁻⁴ S/cm, andoften >10⁻³ S/cm, comparable to those of liquid electrolytes.

These lithium-containing inorganic species can be simply the products orby-products of chemical reactions between the electrolyte (Li salt andsolvent) and a carbon material or a conducting polymer. These reactionsare induced by externally applied current/voltage in an electrochemicalreactor. This will be discussed in more detail later.

In a preferred embodiment, the lithium-containing species may beselected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi,(ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), a combination thereof, ora mixture with a sodium salt (e.g. Na₂CO₃, Na₂O, Na₂C₂O₄, NaOH, NaiX,ROCO₂Na, HCONa, RONa, (ROCO₂Na)₂, (CH₂OCO₂Na)₂, Na₂S, Na_(x)SO_(y)),wherein X=F, Cl, I, or Br, R=a hydrocarbon group (e.g. R=CH—, CH₂—,CH₃CH₂—, etc.), x=0-1, y=1-4. These species, when dispersed in a lithiumion-conducting matrix polymer or bonded by such a polymer, aresurprisingly capable of forming a structurally sound solid stateelectrolyte layer that is sufficiently strong to intercept or stopdendrite penetration, yet maintaining a high lithium ion conductivity.

There are several approaches that can be followed to form a solidcomposite electrolyte containing a lithium ion-conducting polymer andlithium-containing inorganic species selected from Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, Li—SO_(y), or a mixture thereof. These approaches include:

-   -   (a) Solution mixing: This includes dispersion or dissolution of        particles of inorganic lithium-containing species and a lithium        ion-conducting polymer in a solvent to form a solution or        suspension, followed by casting or coating into a preferably        film or sheet form, and solvent removal. Some of these polymers        (e.g. most of the sulfonated polymers) are soluble in water.    -   (b) In situ precipitation from solution state: This includes        preparation of a solution of lithium-containing inorganic        species in a solvent (e.g. dissolution of Li₂CO₃, Li₂C₂O₄, LiOH,        and LiNO₃, separately or in combinations, in water), dipping or        immersing a porous lithium ion-conducting polymer (e.g. a        sulfonated polymer, polyethylene oxide) in this solution, and        allowing precipitation of the inorganic species into pores of        the lithium ion-conducting polymer.    -   (c) Melt mixing: This includes mixing and dispersion of        particles of inorganic lithium-containing species in the melt of        a lithium ion-conducting polymer and then forming of the        resulting composite into a desired shape (e.g. melt mixed in a        twin-screw extruder and then extruded into a sheet, film, or        other desired shapes).    -   (d) Physical or chemical vapor deposition: For instance,        sputtering of inorganic lithium-containing species (lithium        ion-conducting inorganic species in the above list; e.g. Li₂O        and Li₂S) onto surfaces of a lithium ion-conducting polymer.        This polymer is preferably in a thin film form, powder form, or        porous structure that has a high specific surface area to        accommodate the inorganic species deposited thereon. This would        lead to a more uniform dispersion of the inorganic species in        the polymer matrix.    -   (e) Electrochemical decomposition of electrolytes on carbon        surfaces: This includes electrochemical decomposition of        electrolyte solvent/salt and deposition of the desired inorganic        lithium-containing species (as reaction products of the        electrochemical decomposition) onto the surfaces of a carbon        material, followed by dispersion of the inorganic species-coated        carbon particles in a polymer matrix. Alternatively, the        inorganic lithium-containing species are separated from the        carbon substrate and then dispersed in a lithium ion-conducting        polymer using solution mixing or melt mixing.    -   (f) Electrochemical decomposition of electrolytes on polymer        surfaces: This includes electrochemical decomposition of        electrolyte solvent/salt and deposition of the desired inorganic        lithium-containing species (as reaction products of the        electrochemical decomposition) onto the surfaces of a        lithium-conducting polymer. This polymer is preferably in a thin        film form, powder form, or porous structure that has a high        specific surface area to accommodate the inorganic species        deposited thereon.

The carbon material may be selected from multiple sheets/platelets of agraphene material, multiple flakes of exfoliated graphite, carbonnano-fibers, carbon nanotubes, carbon fibers, graphite fibers, carbonblack or acetylene black particles, needle coke, soft carbon particles,hard carbon particles, artificial graphite particles. These particle orfibers preferably have a diameter or thickness less than 10 μm,preferably less than 1 μm, further preferably less than 200 nm, and mostpreferably less than 100 nm.

The carbon material can be produced by several processes. For instance,thin films of amorphous carbon can be deposited on a solid substratesurface using chemical vapor deposition of hydrocarbon gas introducedinto a chamber at a temperature of 400-1,200° C. under a hydrogen ornoble gas atmosphere. Alternatively, amorphous carbon can be produced bysputtering of carbon atoms or clusters of C atoms onto a solid substratesurface from a carbon target in a vacuum chamber. The resultingamorphous carbon films, after being deposited with lithium-containinginorganic species, can then be peeled off from the substrate to obtainfree-standing films. The lithium-containing inorganic material-coatedcarbon films are then chopped into small pieces and then dispersed in asulfonated polymer via solution mixing or melt mixing. Alternatively,the lithium-containing inorganic material-coated carbon film can bedeposited with a layer of a lithium ion-conducting polymer prior tobeing milled into small particles. Small particles of lithium-containinginorganic material/carbon/polymer are then processed into a sheet orfilm for use as a solid state electrolyte. The proportion of carbon mustbe minimized to the extent that the resulting composite solidelectrolyte is lithium ion-conducting, but not electronicallyconducting.

Carbon films may also be produced by pyrolyzation of polymer films(including thermoplastic films, thermoset films, coal tar pitch films,petroleum pitch films, etc., free-standing or coated on a solidsurface), typically at an initial oxidation temperature of 250-350° C.(e.g. for polyacrylonitrile, PAN), followed by a carbonization treatmentat 500-1,500° C. For other polymer films, heat treatments can godirectly into the range of 500-1,500° C. without a pre-oxidation (e.g.phenolic resin). These films are herein referred to as polymeric carbonor carbonized resin films. There is no restriction on the kind ofpolymer or pitch material that can be pyrolyzed to produce the neededcarbon matrix; but, preferably, the resin or pitch has a carbon yield ofat least 20% (more preferably at least 30% and most preferably from 40%to approximately 75%). The carbon films are then used as a workingelectrode for receiving lithium-containing inorganic species produced bythe electrochemical decomposition of electrolytes.

Thin films of a polymer matrix composite (e.g. a mixture of phenolicresin+CNTs and/or graphene sheets) can be prepared in a free-standingform or coated on a solid substrate. This can be made by a solventmixing or melt mixing procedure that is well-known in the art. Thisresin matrix composite is then subjected to the heat treatments asdescribed above (e.g. at a temperature in the range of 500-1,500° C.) toobtain carbon matrix composites. The carbon composite films are thenused as a working electrode for receiving lithium-containing inorganicspecies produced by the electrochemical decomposition of electrolytes.

Alternatively, one can prepare a sheet of porous non-woven, mat, paper,foam, or membrane of a carbon/graphite reinforcement material (e.g.graphene sheets, expanded graphite flakes, CNTs, carbon nano-fibers,etc.) by using any known process. This porous structure is theninfiltrated with carbon using chemical vapor deposition (CVD),sputtering, or chemical vapor infiltration (CVI) to obtain a carbonmatrix composite. Further alternatively, this porous structure can beimpregnated with a resin or pitch material and the resulting compositebe pyrolyzed to obtain a carbon matrix composite. The porous carbonsheets are then used as a working electrode for receivinglithium-containing inorganic species produced by the electrochemicaldecomposition of electrolytes.

The carbon matrix films or carbon matrix composite films can be solid orporous. The pores eventually will be substantially filled withlithium-containing species. The lithium-containing species resultingfrom electrochemical decomposition of electrolytes (to be explainedlater) can be attached to the carbon matrix or the carbon/graphitereinforcement particles/fibers/nanotubes.

In addition to or as an alternative to the carbon/graphite reinforcementphase, a filler in the form of multiple particles may be dispersed inthe amorphous carbon or polymeric carbon matrix. The filler may beselected from a metal oxide, metal carbide, metal nitride, metal boride,metal dichalcogenide, or a combination thereof. In an embodiment, thefiller is selected from an oxide, dichalcogenide, trichalcogenide,sulfide, selenide, or telluride of niobium, zirconium, molybdenum,hafnium, tantalum, tungsten, titanium, vanadium, chromium, cobalt,manganese, iron, or nickel in a nanowire, nano-disc, nano-ribbon, ornano platelet form.

Preferably, the filler is selected from nano discs, nano platelets, ornano sheets of an inorganic material selected from: (a) bismuth selenideor bismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof; wherein the discs, platelets, or sheets havea thickness less than 100 nm. These 2D nano materials are found to bevery effective in helping to stop dendrite penetration; however, theyare normally not very permeable to lithium ions or sodium ions. Hence,they must be dispersed in a carbon matrix that is permeable to lithiumor sodium ions.

Most preferably, a lithium ion-conducting polymer (e.g. a sulfonatedpolymer or its mixture, with or without a filler) can be made into athin film, paper sheet, fiber, web, grid, non-woven mat, and otherporous structural shape, which is then deposited with thelithium-containing inorganic species produced by electrochemicaldecomposition of electrolytes.

Electrochemical Decomposition of Electrolytes:

The preparation of desired inorganic lithium-containing species may beconducted in an electrochemical reactor, which is an apparatus similarto an electrode plating system but operated in very distinct conditions.In this reactor, a sulfonated conducting polymer and/or an amorphouscarbon or polymeric carbon matrix (with or without a carbon/graphitereinforcement material), in the form of a mat, paper, film, etc., isused as a working electrode and lithium sheet as a counter electrode.Contained in the reactor is an electrolyte composed of a lithium saltdissolved in a solvent (e.g. 1M LiPF₆ dissolved in a mixture of ethylenecarbonate (EC) and dimethyl carbonate (DMC) at a 1:1 ratio by volume). Acurrent is then imposed between these two electrodes (lithium sheetelectrode and the carbon working electrode).

The sulfonated polymer or carbon material (e.g. carbon matrix and thecarbon/graphite reinforcement material) in the working electrode aregalvanostatically discharged (e.g. Li ions being sent to and captured bythese polymer and/or carbon material and charged (Li ions released bythe polymer or carbon material) in the voltage range from 0.01V to 4.9Vat the current densities of 100-1000 mA/g following a voltage-currentprogram similar to what would be used in a lithium-ion battery. However,the system is intentionally subjected to conditions conducive tooxidative degradation of electrolyte (e.g. close to 0.01-1.0 V vs.Li/Li⁺) or reductive degradation of electrolyte (4.1-4.9 V vs. Li/Li⁺)for a sufficient length of time. The degradation products react with Li⁺ions, Li salt, functional groups (if any) or carbon atoms on/in thecarbon matrix or carbon/graphite reinforcement to form thelithium-containing species that also chemically bond to the carbonmatrix or composite. We have also surprisingly observed that, when asulfonated polymer or polymer mixture is subjected to comparableelectrochemical treatment conditions, various desired lithium-containinginorganic species are formed on polymer surfaces.

The chemical compositions of the lithium-containing species are governedby the voltage range, the number of cycles (from 0.01 V to 4.9 V, andback), solvent type, lithium salt type, chemical composition ofcarbon/graphite phase (e.g. % of O, H, and N attached to CNTs, CNFs,exfoliated graphite flakes, graphene sheets, etc.), and electrolyteadditives (e.g. LiNO₃, if available). The morphology, structure andcomposition of carbon/graphite reinforcement phase, the amorphous carbonmatrix, the lithium-containing species that are bonded to the carbonmaterial or sulfonated polymer can be characterized by scanning electronmicroscope (SEM), transmission electron microscope (TEM), Ramanspectrum, X-ray diffraction (XRD), Fourier Transform InfraredSpectroscopy (FTIR), elemental analysis, and X-ray photoelectronspectroscopy (XPS).

The decomposition of non-aqueous electrolyte leads to the formation oflithium chemical compounds that bond to surface/ends of CNTs, graphenesurfaces and edges, functional groups of chemically treated carbon blackparticles, a conducting polymer, etc. The reasons why the non-aqueouselectrolyte is decomposed during discharge-charge cycling in anelectrochemical reactor may be explained as follows. As illustrated inFIG. 2, in an electrochemical reactor system where there are a cathodeand an anode in contact with an electrolyte, the thermodynamic stabilityof the electrolyte is dictated by the relative electron energies of thetwo electrodes relative to the energy level of the non-aqueouselectrolyte. The anode is potentially a reductant, and the cathode anoxidant. The two electrodes are typically electronic conductors and, inthis diagram, their electrochemical potentials are designated as μ_(A)and μ_(C) (or Fermi energies ε_(F)), respectively. The energyseparation, E_(g), between the lowest unoccupied molecular orbital(LUMO) and the highest occupied molecular orbital (HOMO) of theelectrolyte is the stable electrochemical window of the electrolyte. Inother words, in order for the electrolyte to remain thermodynamicallystable (i.e. not to decompose), the electrochemical potential of theanode (μ_(A)) must be maintained below the LOMO and μ_(C) of the cathodemust be above the HOMO.

From the schematic diagram of FIG. 2, we can see that an anode withμ_(A) above the LUMO and a cathode with μ_(C) below the HOMO will reduceand oxidize the electrolyte, respectively, unless a passivating film isformed that creates a barrier to electron transfer between the anode andelectrolyte or between the cathode and the electrolyte. In the presentlyinvented method, an external current/voltage is intentionally appliedover the anode and the cathode to bias their respective electrochemicalpotential levels so that the electrolyte can go outside of the stableelectrochemical potential window, undergoing oxidative and/or reductivedegradation. The degradation products are reactive species that reactamong themselves and with the functional groups or active atoms of theelectrode polymer or carbon material, forming a mass oflithium-containing species that bond to the conducting polymer or thecarbon material.

For the list of lithium salts and solvents investigated, theelectrolytes have an oxidation potential (HOMO) at about 4.7 V and areduction potential (LUMO) near 1.0 V. (All voltages in thisspecification are with respect to Li⁺/Li). We have observed that thechemical interaction of Li⁺ ions with graphene planes or edges occur atabout 0.01-0.8 V, so electrolytes are prone to reductive degradation inthe voltage range of 0.01-0.8 V. By imposing a voltage close to 4.7volts, the electrolytes are also subject to oxidative degradation. Thedegradation products spontaneously react with chemical speciesassociated with the carbon matrix and/or reinforcement materials (e.g.graphene planes or edges), forming a material phase that bonds togetherwith carbon matrix and/or reinforcement materials during thecharge-discharge cycling (electrolyte reduction-oxidation cycling). Ingeneral, these lithium-containing species are not electricallyconducting and, hence, these reactions can self-terminate to formessentially a passivating phase.

The electrolytes that can be used in this electrochemical decompositionreactor may be selected from any lithium or sodium metal salt that isdissolvable in a solvent to produce an electrolyte. Preferably, themetal salt is selected from lithium perchlorate (LiClO₄), lithiumhexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄), lithiumhexafluoroarsenide (LiAsF₆), lithium trifluoro-metasulfonate (LiCF₃SO₃),bis-trifluoromethyl sulfonylimide lithium (LiN(CF₃SO₂)₂), lithiumbis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF₂C₂O₄),lithium oxalyldifluoroborate (LiBF₂C₂O₄), lithium nitrate (LiNO₃),Li-Fluoroalkyl-Phosphates (LiPF₃(CF₂CF₃)₃), lithiumbisperfluoro-ethysulfonylimide (LiBETI), lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide (LiTFSI), or a combination thereof.It may be noted that these metal salts are also commonly used in theelectrolytes of rechargeable lithium batteries.

The electrolytes used in this electrochemical reactor may contain asolvent selected from 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME),tetraethylene glycol dimethylether (TEGDME), poly(ethylene glycol)dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE),2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC),dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate(DEC), ethyl propionate, methyl propionate, propylene carbonate (PC),gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA),propyl formate (PF), methyl formate (MF), toluene, xylene, methylacetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC),allyl ethyl carbonate (AEC), a hydrofluoroether, a room temperatureionic liquid solvent, or a combination thereof. These solvents are alsocommonly used in the electrolytes of rechargeable lithium or sodiumbatteries.

The porous structure (e.g. paper, mat, foam, etc. of a carbon materialor a sulfonated polymer) is subjected to the electrochemicaldecomposition treatment to form the lithium-containing species in theinterstitial spaces, gaps, or voids (if any) but bonded to the porewalls, or simply bonded to surfaces of the carbon matrix or sulfonatedpolymer to form a solid state electrolyte material.

For industrial-scale production of the presently invented solid stateelectrolyte, the electrochemical decomposition treatment may be carriedout in a roll-to-roll manner. In an embodiment, the continuous-lengthpaper (or mat, foam, membrane, etc.) of a carbon material or sulfonatedpolymer (as an example of lithium ion-conducting polymer) may be unwoundfrom a feeder roller, and moved to enter an electrochemical treatmentzone (essentially an electrochemical decomposition reactor) containingan electrolyte therein. A lithium metal electrode is immersed in thiselectrolyte and the paper is also electrically wired as the workingelectrode. The paper is moved at a controlled speed to give enough timefor electrochemical decomposition of the electrolyte to occur. Thepaper, impregnated with and/or bonded by the decomposition products, isthen wound up on a take-up roller. This roll-to-roll or reel-to-reelprocess can be easily scaled up and automated for mass production of thepresently invented solid electrolyte products.

In an alternative embodiment, the continuous-length paper may be unwoundfrom a feeder roller, deposited with some lithium metal (e.g. usingphysical vapor deposition or sputtering of Li) while the carbon orsulfonated polymer paper is in a dry state (before contactingelectrolyte). The Li-deposited paper is then moved to enter anelectrochemical treatment zone containing an electrolyte therein. Assoon as the Li-paper layer enters the electrolyte, essentiallyshort-circuiting occurs between the carbonaceous or polymeric paper andLi. In other words, the paper “electrode” is essentially placed in anelectrochemical potential that is 0 V with respect to Li⁺/Li, subjectingthe electrolyte to a reductive decomposition and enabling decompositionproducts to react with carbon or polymer. Optionally, a lithiumelectrode is implemented and immersed in this electrolyte and the paperis also electrically wired as the working electrode. Such an arrangementaids in continuing the electrochemical decomposition of electrolytes andformation of the Li-containing species. The carbon or polymer paper ismoved at a controlled speed to give enough time for electrochemicaldecomposition of the electrolyte to occur. The paper, impregnated withand bonded by the decomposition products, is then wound up on a take-uproller. Again, this roll-to-roll process is highly scalable and can befully automated for cost-effective production of the desired solid stateelectrolyte product.

In yet another embodiment, a layer of alkali metal anode (e.g. astand-along Li foil, or a nano-structured current collector depositedwith some lithium metal) is deposited with a layer of carbon or polymer(e.g. using a spraying procedure) up to a thickness from 2 nm to 20 μmto form a two-layer or three-layer laminate. Alternatively, a layer ofalkali metal anode (containing one layer of Li foil alone or a two-layerconfiguration composed of a nano-structured current collector and alayer of Li metal, for instance) is directly laminated with a layer ofpre-fabricated sulfonated polymer paper/mat to form a 2-layer or 3-layerlaminate. This laminate is then combined with an anode and a cathode toform a multiple-layer battery structure.

The solid state electrolyte of the instant invention typically exhibitsa lithium ion conductivity from 2.5×10⁻⁵ S/cm to 5.5×10⁻³ S/cm, and moretypically from 1.0×10⁻⁴ S/cm to 2.5×10⁻³ S/cm. There is no restrictionon the thickness of the solid electrolyte between an anode and acathode; but for practical purposes, the solid electrolyte layerpreferably has a thickness from 2 nm to 20 μm, more preferably from 10nm to 10 μm, and most preferably from 100 nm to 1 μm.

The cathode active material in this rechargeable alkali metal batterymay be selected from sulfur, selenium, tellurium, lithium sulfide,lithium selenide, lithium telluride, sodium sulfide, sodium selenide,sodium telluride, a chemically treated carbon or graphite materialhaving an expanded inter-graphene spacing d₀₀₂ of at least 0.4 nm, or anoxide, dichalcogenide, trichalcogenide, sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, vanadium, chromium, cobalt, manganese, iron, nickel, or acombination thereof. Preferred cathode active materials includenon-lithiated and slightly lithiated compounds having relatively highlithium or sodium storage capacities, such as TiS₂, MoS₂, MnO₂, CoO₂,and V₂O₅.

A novel family of 2D metal carbides or metal carbonides, now commonlyreferred to as MXenes, can be used as a cathode active material. MXenescan be produced by partially etching out certain elements from layeredstructures of metal carbides such as Ti₃AlC₂. For instance, an aqueous 1M NH₄HF₂ was used at room temperature as the etchant for Ti₃AlC₂.Typically, MXene surfaces are terminated by O, OH, and/or F groups,which is why they are usually referred to as M_(n+1)X_(n)T_(x), where Mis an early transition metal, X is C and/or N, T represents terminatinggroups (O, OH, and/or F), n=1, 2, or 3, and x is the number ofterminating groups. The MXene materials investigated include Ti₂CT_(x),(Ti_(0.5), Nb_(0.5))₂CT_(x), Nb₂CT_(x), V₂CT_(x), Ti₃C₂T_(x), (V_(0.5),Cr_(0.5))₃C₂T_(x), Ti₃CNT_(x), Ta₄C₃T_(x), and Nb₄C₃T_(x).

In an embodiment, the cathode layer contains an air cathode and thebattery is a lithium-air battery. In another embodiment, the cathodeactive material is selected from sulfur or lithium polysulfide and thebattery is a lithium-sulfur battery. In yet another embodiment, thecathode active material may be selected from an organic or polymericmaterial capable of capturing or storing lithium ions (e.g. viareversibly forming a redox pair with lithium ion).

The electrolytic salts to be incorporated in a sulfonated polymer toform a solid state electrolyte for a lithium secondary battery may beselected from a lithium salt such as lithium perchlorate (LiClO₄),lithium hexafluorophosphate (LiPF₆), lithium borofluoride (LiBF₄),lithium hexafluoroarsenide (LiAsF₆), lithium trifluoro-metasulfonate(LiCF₃SO₃), bis-trifluoromethyl sulfonylimide lithium [LiN(CF₃SO₂)₂],lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate(LiBF₂C₂O₄), lithium oxalyldifluoroborate (LiBF₂C₂O₄), lithium nitrate(LiNO₃), Li-Fluoroalkyl-Phosphates (LiPF3(CF₂CF₃)₃), lithiumbisperfluoroethysulfonylimide (LiBETI), an ionic liquid salt, and theirsodium counterparts. Among them, LiPF₆, LiBF₄ and LiN(CF₃SO₂)₂ arepreferred.

The ionic liquid (if containing a lithium salt or itself being a lithiumsalt) may also be electrochemically decomposed to produce the desiredlithium-containing inorganic species. Ionic liquids are low meltingtemperature salts that are in a molten or liquid state when above adesired temperature. For instance, a salt is considered as an ionicliquid if its melting point is below 100° C. If the melting temperatureis equal to or lower than room temperature (25° C.), the salt isreferred to as a room temperature ionic liquid (RTIL). The IL salts arecharacterized by weak interactions, due to the combination of a largecation and a charge-delocalized anion. This results in a low tendency tocrystallize due to flexibility (anion) and asymmetry (cation).

A typical and well-known ionic liquid is formed by the combination of a1-ethyl-3-methylimidazolium (EMI) cation and anN,N-bis(trifluoromethane)sulphonamide (TFSI) anion. This combinationgives a fluid with an ionic conductivity comparable to many organicelectrolyte solutions and a low decomposition propensity and low vaporpressure up to −300-400° C. This implies a generally low volatility andnon-flammability and, hence, a much safer electrolyte for batteries.

Ionic liquids are basically composed of organic ions that come in anessentially unlimited number of structural variations owing to thepreparation ease of a large variety of their components. Thus, variouskinds of salts can be used to design the ionic liquid that has thedesired properties for a given application. These include, among others,imidazolium, pyrrolidinium and quaternary ammonium salts as cations andbis(trifluoromethanesulphonyl) imide, bis(fluorosulphonyl)imide, andhexafluorophosphate as anions. Based on their compositions, ionicliquids come in different classes that basically include aprotic, proticand zwitterionic types, each one suitable for a specific application.

Common cations of room temperature ionic liquids (RTILs) include, butnot limited to, tetraalkylammonium, di-, tri-, andtetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium,dialkylpiperidinium, tetraalkylphosphonium, and trialkylsulfonium.Common anions of RTILs include, but not limited to, BF₄ ⁻, B(CN)₄ ⁻,CH₃BF₃ ⁻, CH2CHBF₃ ⁻, CF₃BF₃ ⁻, C₂F₅BF₃ ⁻, n-C₃F₇BF₃ ⁻, n-C₄F₉BF₃ ⁻, PF₆⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, N(COCF₃)(SO₂CF₃)⁻, N(SO₂F)₂ ⁻,N(CN)₂ ⁻, C(CN)₃ ⁻, SCN⁻, SeCN⁻, F(HF)_(2.3) ⁻, etc. Relativelyspeaking, the combination of imidazolium- or sulfonium-based cations andcomplex halide anions such as AlC₄ ⁻, BE₄ ⁻, CF₃CO₂ ⁻, CF₃SO₃ ⁻, NTf₂ ⁻,N(SO₂F)₂ ⁻, or F(HF)_(2.3) ⁻ results in RTILs with good workingconductivities.

At the anode side, lithium metal may be a layer of Li metal or alloy(>₇₀% by weight of Li, preferably >80%, and more preferably >90%).Alternatively, the Li metal or alloy may be supported by anano-structure composed of conductive nano-filaments. For instance,multiple conductive nano-filaments are processed to form an integratedaggregate structure, preferably in the form of a closely packed web,mat, or paper, characterized in that these filaments are intersected,overlapped, or somehow bonded (e.g., using a binder material) to oneanother to form a network of electron-conducting paths. The integratedstructure has substantially interconnected pores to accommodateelectrolyte. The nano-filament may be selected from, as examples, acarbon nano fiber (CNF), graphite nano fiber (GNF), carbon nano-tube(CNT), metal nano wire (MNW), conductive nano-fibers obtained byelectro-spinning, conductive electro-spun composite nano-fibers,nano-scaled graphene platelet (NGP), or a combination thereof. Thenano-filaments may be bonded by a binder material selected from apolymer, coal tar pitch, petroleum pitch, meso-phase pitch, coke, or aderivative thereof.

Nano fibers may be selected from the group consisting of an electricallyconductive electro-spun polymer fiber, electro-spun polymernanocomposite fiber comprising a conductive filler, nano carbon fiberobtained from carbonization of an electro-spun polymer fiber,electro-spun pitch fiber, and combinations thereof. For instance, anano-structured electrode can be obtained by electro-spinning ofpolyacrylonitrile (PAN) into polymer nano-fibers, followed bycarbonization of PAN. It may be noted that some of the pores in thestructure, as carbonized, are greater than 100 nm and some smaller than100 nm.

In summary, a possible lithium metal cell may be comprised of an alkalimetal layer (e.g. Li foil, etc.), an anode current collector (e.g. Cufoil and/or a nano-structure of interconnected conductive filaments), asolid state electrolyte phase, a cathode, and an optional cathodecurrent collector (e.g. Al foil and/or or a nano-structure ofinterconnected conductive filaments, such as graphene sheets and carbonnano-fibers).

The following examples serve to illustrate the preferred embodiments ofthe present invention and should not be construed as limiting the scopeof the invention:

Example 1: Synthesis of Sulfonated Polyaniline (S-PANi)

The chemical synthesis of the S-PANi polymers was accomplished byreacting polyaniline with concentrated sulfuric acid. The procedure wassimilar to that used by Epstein, et al. (U.S. Pat. No. 5,109,070, Apr.28, 1992). The resulting S-PANi can be represented by the followingFormula 1, with R₁, R₂, R₃, and R₄ group being H, SO₃ ⁻ or SO₃H (R₅=H)with the content of the latter two being varied between 30% and 75%(i.e., the degree of sulfonation varied between 30% and 75%).

The lithium ion conductivity of these SO₃ ⁻ or SO₃H-based S-PANicompositions was in the range of 8.5×10⁻⁵ S/cm to 4.6×10⁻³ S/cm andtheir electron conductivity in the range of 0.1 S/cm to 0.5 S/cm whenthe degree of sulfonation was from approximately 30% to 75% (with ybeing approximately 0.4-0.6).

The solid state electrolyte was obtained by dissolving S-PANi in wateror acetonitrile to form a polymer-water or polymer-solvent solution anddissolving commercially available Li₂CO₃, Li₂C₂O₄, LiOH, LiNO₃, andLi₂SO₄ and their mixtures of various proportions in water/solvent toform lithium salt solutions. The S-PANi-water/solvent solution andvarious separate lithium salt solutions were then mixed together inseveral proportions to obtain mixture solutions, which were cast intothin films and then dried to produce solid state electrolyte filmshaving a thickness from 150 nm to 15 μm.

In several samples, a mixture solution composed of lithium-containinginorganic species and PANi dissolved in water/solvent was sprayed onsurfaces of a pre-fabricated sulfur cathode electrode (explained in anexample later) to form a solid state electrolyte layer having 5-25% byweight of Li₂CO₃—Li₂SO₄ (50/50) and 75-95% PANi. This electronicallyconducting layer (2.5 μm thick) was used to eliminate the shuttlingeffect of sulfur and lithium sulfide in a Li—S cell. In such a lithiumcell, a thin layer of sulfonated PEEK (lithium ion-conducting, but notelectron-conducting) 3 μm thick was implemented on the surface of a Lifoil at the anode side. As a result a hybrid solid electrolyte was usedin this Li—S cell.

Example 2: Sulfonated Conducting Polymers (Sulfonated Polypyrrole,S-Ppy)

A sulfonated pyrrole-based polymer (with X=NH and Y=SO₃ ⁻, m=1, and A=Hin the following formula) was synthesized by following a procedureadapted from Aldissi, et al., U.S. Pat. No. 4,880,508, Nov. 14, 1989.

Approximately 5.78 g of the resulting sulfonated pyrrole-based polymerwas dissolved in 100 ml of distilled water. Then, 105 ml of 0.98%aqueous LiOH and LiNO₃ (50/50) were added to the sulfonated polypyrrole(S-PPy)-polyethylene oxide (PEO) water suspension over the course of 60minutes while stirring constantly. The resulting polypyrrole-inorganicspecies composite was used as a solid state electrolyte.

Example 3: Preparation of Poly (Alkyl Thiophene) as anElectron-Conducting Component of a Mixture

Water-soluble conductive polymers having a thiophene ring (X=sulfur) andalkyl groups containing 4 carbon atoms (m=4) in the above Formula 2 wereprepared, according to a method adapted from Aldissi, et al. (U.S. Pat.No. 4,880,508, Nov. 14, 1989). The surfactant molecules of thesepolymers were sulfonate groups with sodium. Conductivity of this polymerin a self-doped state were from about 10⁻³ to about 10⁻² S/cm. Whennegative ions from a supporting electrolyte used during synthesis wereallowed to remain in the polymer, conductivities up to about 50 S/cmwere observed.

A doped poly (alkyl thiophene) (PAT) with Y=SO₃H and A=H in Formula 6that exhibited an electron conductivity of 12.5 S/cm was dissolved inwater. A sulfonated poly(ether ether ketone)-based material called poly(phthalazinon ether sulfone ketone) (PPESK), having a degree ofsulfonation of approximately 93%, was soluble in an aqueous hydrogenperoxide (H₂O₂) solution. A water solution of 3 wt. % poly (alkylthiophene) and an aqueous H₂O₂ solution of 3 wt. % sulfonated PPESK wasmixed at several PPESK-to-PAT ratios and stirred at 70° C. to obtainseveral polymer blend solution samples.

Samples of poly (alkyl thiophene)-PPESK mixtures (containing lithiumsalt) in a thin film form were obtained by casting the aforementionedsolutions onto a glass plate, allowing water to evaporate. The lithiumand electron conductivity values of the resulting solid samples werethen measured at room temperature. The results indicate that goodelectron and lithium ion conductivities can be obtained within the rangeof 30-70% PPESK. It may be noted that poly (alkyl thiophene) can gothrough the complexing and reduction procedures to obtain a watersoluble polymer. In this case, PPESK can be used to improve the lithiumion conductivity.

Example 4: Bi-Cyclic Conducting Polymer as a Lithium Ion-ConductingPolymer

The preparation of conductive polymers represented by Formula 3 having Hfor both R₁ and R₂, S for X, and H⁺ for M was accomplished by followinga procedure suggested by Saida, et al. (U.S. Pat. No. 5,648,453, Jul.15, 1997).

These polymers exhibit electronic conductivity in the range of 5×10⁻²S/cm to 1.4 S/cm and lithium ion conductivity of 6.5×10'S/cm 2.5×10⁻²S/cm.

Six polymer blends were prepared from such a bi-cyclic polymer (electronconductivity Φ_(c)=1.1 S/cm and lithium ion conductivity Φ_(p)=3.5×10⁻³S/cm) and approximately 50% by wt. of the following lithium-conductingpolymers: poly (perfluoro sulfonic acid) (PPSA), sulfonated PEEK(S-PEEK), sulfonated polystyrene (S-PS), sulfonated PPESK, sulfonatedpolyimide (S-PI), and sulfonated polyaniline (S-PANi). Theconductivities of the resulting polymer blends are Φ_(c)=0.22 S/cm andΦ_(p)=2.8×10⁻³ S/cm for (bi-cyclic+PPSA), Φ_(c)=0.2 S/cm andΦ_(p)=3.6×10⁻³ S/cm for (bi-cyclic+S-PEEK), Φ_(c)=0.23 S/cm andΦ_(p)=5.6×10⁻³ S/cm for (bi-cyclic+S-PS), Φ_(c)=0.19 S/cm andΦ_(p)=4.6×10⁻³ S/cm for (bi-cyclic+S-PPESK), Φ_(c)=0.21 S/cm andΦ_(p)=2.3×10⁻³ S/cm for (bi-cyclic+S-PI), and Φ_(c)=0.75 S/cm andΦ_(p)=1.4×10⁻³ S/cm for (bi-cyclic+S-PANi), The lithium ion conductivityvalues are all within the acceptable ranges for these polymer blends tobe a good matrix material for embedding the lithium-containing inorganicspecies in a solid state electrolyte composition.

Example 5: Sulfonation of Electrically Non-Conducting Polymers

Polytetrafluoroethylene (PTFE), polysulfone (PSf), poly (ether etherketone) (PEEK), polyimide (PI), and styrene-butadiene copolymers (SB)were separately immersed in a concentrated sulfuric acid (95%+5% water)at 65-90° C. for 4-48 hours to obtain sulfonated polymers. Thesesulfonated polymers were found to be electrically insulating (<10⁻⁸S/cm), but lithium ion-conducting (typically 3×10⁻⁵ S/cm-4.5×10⁻³ S/cm,depending on the degree of sulfonation).

These highly sulfonated polymers alone, or its mixture with a lithiumsalt or lithium-containing inorganic species, can be used as a solidstate electrolyte. It is unexpected for us to discover that a simplemixture of a sulfonated polymer and a commonly used lithium salt (e.g.LiClO₄, LiPF₆, LiBF₄, LiAsF₆, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiBOB, LiBF₂C₂O₄,LiBF₂C₂O₄, LiPF₃(CF₂CF₃)₃, LiBETI, and LiTFSI, just to name a few) makesan exceptional solid-state electrolyte that can be easily andcost-effectively prepared and that are highly lithium ion-conducting.

Alternatively, these sulfonated polymers can be mixed with thelithium-containing inorganic species that are not normally used as alithium salt in lithium-ion battery industry (e.g. Li₂CO₃, Li₂O,Li₂C₂O₄, LiOH, LiX, ROCO₂Li, HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂,Li₂S, Li_(x)SO_(y)) to form a solid state electrolyte.

Example 6: Preparation of Lithium-Containing Inorganic Species onSurfaces of a Carbon or Sulfonated Polymer

Two approaches were followed to produce lithium-containing inorganicspecies on surfaces of a carbon or sulfonated polymer layer viaelectrochemical decomposition of lithium salt-solvent electrolytes.

The first entails preparing an electrochemical electrode composed of asulfonated conductive polymer in a porous foam structure using achemical foaming agent or a freeze-drying procedure. Some of theseelectrodes were deposited with a layer of amorphous carbon, 0.5-3 μmthick using sputtering or low-temperature CVD. The porous electrode(with or without a carbon coating) and a lithium foil (20 μm thick) werethen laminated together. This two-layer structure was then immersed in alithium salt-solvent solution (e.g. LiClO₄, LiPF₆, and/or LiBF₄, in anorganic solvent, PC, EC, or DEC). This would create an internal shortcircuiting situation (since carbon or sulfonated polymer and lithium areoriginally at different electrochemical potential levels), inducingdecomposition of electrolyte that produces lithium-containing inorganicspecies on surfaces of carbon or conducting polymer. After 20-120minutes, the polymer layer (now coated or impregnated with somelithium-containing inorganic species (e.g. Li₂CO₃, Li₂O, Li₂C₂O₄, LiCl,LiF, Li₄B, or their mixtures). The coated or impregnated polymer is thendirectly melted and re-cast into a film, or milled into small pieces andthen mixed with additional amounts of Li₂CO₃, Li₂O, Li₂C₂O₄, LiCl, LiF,and/or Li₄B (if so desired) and/or other type of sulfonated polymer andextruded into composite films. These films are used as solid stateelectrolyte.

The second approach is described in Example 7 below.

Example 7: Electrochemical Preparation of Lithium-Containing InorganicSpecies on a Carbon Material or a Conducting Polymer

The preparation of solid state electrolytes was carried out in anelectrochemical reactor, an apparatus very similar to an electrodeplating system. In this reactor, a layer of carbon matrix, carbon matrixcomposite structure (in the form of a mat, paper, film, etc.), orconducting polymer (prepared in Examples 1, 2 and 5) was used as aworking electrode and lithium sheet as both the counter and referenceelectrodes. Inside the reactor is an electrolyte composed of 1M LiPF₆dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate(DMC) (1:1 by volume), as an example. The carbon material or conductingsulfonated polymer layer in the working electrode was galvanostaticallydischarged (Li ions being sent to this working electrode) and charged(Li ions partially released by this working electrode) in the voltagerange from 0.01V to 4.9V at the current densities of 100-1000 mA/gfollowing a voltage-current program similar to what would be used in alithium-ion battery. However, the system was intentionally subjected toconditions conducive to oxidative degradation of electrolyte (close to0.01-1.0 V vs. Li/Li⁺) or reductive degradation of electrolyte (e.g.4.1-4.9 V vs. Li/Li⁺) for a sufficient length of time. The degradationproducts react with Li⁺ ions, Li salt, functional groups (if any) orcarbon atoms on the carbon material or sulfonated polymer to form thelithium-containing species that are bonded to the working electrodematerial.

The chemical compositions of the lithium-containing species are governedby the voltage range, the number of cycles (from 0.01 V to 4.9 V, andback), solvent type, lithium salt type, chemical composition of carbonmatrix and the carbon/graphite reinforcement phase (e.g. % of O, H, andN), and electrolyte additives (e.g. LiNO₃), if available.

The morphology, structure and composition of the carbon matrix,composites, the lithium-containing species that are bonded to carbonmatrix or composites were characterized by scanning electron microscope(SEM), transmission electron microscope (TEM), Raman spectrum, X-raydiffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Anextensive investigation that covers a broad range of lithium salts,solvents, and additives lead to the following discoveries:

A wide range of lithium-containing inorganic species were formed in acontrolled manner and these species were well-bonded to the carbonmaterial or sulfonated polymer. The resulting lithium chemical species,when dispersed in or bonded by a sulfonated polymer, are of structuralintegrity, robust enough to intercept metal dendrites or stop dendritepenetration through this solid state electrolyte.

In these working electrode layers, species (CH₂OCO₂Li)₂ is atwo-electron reduction product of ethylene carbonate (EC) in an EC-basedelectrolytes. ROCO₂Li species are present between carbon or graphiticmaterial (or a conducting polymer) in electrolytes containing propylenecarbonate (PC), especially when the concentration of PC in theelectrolyte is high. Li₂CO₃ is present on carbon matrix orcarbon/graphite reinforcement surfaces in EC or PC based electrolyteswhen a higher voltage is imposed for an extended period of time. Thisspecies also appear as a reaction product of semi-carbonates with HF orwater or CO₂. ROLi is produced on a carbon material in etherelectrolytes such as tetrahydrofuran (THF), dimethyl carbonate (DMC), orethyl methyl carbonate (EMC) as an electrochemical reduction product atan electrochemical potential lower than 0.5 V vs. Li/Li⁺.

LiF is readily formed in electrolytes containing fluorinated salts suchas LiAsF₆, LiPF₆, and LiBF₄, as a salt reduction product. Li₂O is adegradation product of Li₂CO₃. LiOH is formed when a small butcontrolled amount of water is added to the reactor. Species such asLi₂C₂O₄, Li carboxylate, Li methoxide, are formed in electrolytescontaining 1-2 M of LiPF₆ in EC:EMC (e.g. at a 3:7 ratio). HCOLi isformed when methyl formate is used as a co-solvent or additive in theelectrolyte.

The lithium-containing inorganic species are typically deposited onsurfaces of a polymer or impregnated into pores of a conductive porouspolymer. The coated or impregnated polymer is then directly melted andre-cast into a film, or milled into small pieces and then mixed withadditional amounts of Li₂CO₃, Li₂O, Li₂C₂O₄, LiCl, LiF, and/or Li₄B (ifso desired) and/or other type of sulfonated polymer and extruded intocomposite films. Alternatively, the coated or impregnated carbonmaterial is then milled into small pieces and then mixed with additionalamounts of Li₂CO₃, Li₂O, Li₂C₂O₄, LiCl, LiF, and/or Li₄B (if so desired)and a sulfonated polymer (as a matrix or binder) and extruded intocomposite films These films are used as solid state electrolyte.

Table 1 below demonstrates that the presently invented solid stateelectrolytes exhibit lithium ion conductivity values that are superiorto those of known solid state electrolytes, either ceramic orpolymer-based. These conductivity values were measured by the well-knownelectric impedance method.

TABLE 1 Lithium ion conductivity of various solid state electrolytecompositions. Lithium-conducting Sample Lithium-containing polymer(sulfonated No. inorganic species polymer) Li-ion conductivity (S/cm)A1-1 Li₂CO₃ + (CH₂OCO₂Li)₂ S-PANi (23-100% by 4.6 × 10⁻⁴ to 4.8 × 10⁻³S/cm wt.) (also see FIG. 3) A1-2 Li₂CO₃ + (CH₂OCO₂Li)₂ S-PEEK (12-100%by 6.4 × 10⁻⁴ to 3.6 × 10⁻³ S/cm wt.) A1-3 Li₂CO₃ + (CH₂OCO₂Li)₂ S-PTFE2.2 × 10⁻⁴ to 1.2 × 10⁻³ S/cm A1-4 Li₂CO₃ + (CH₂OCO₂Li)₂ S-PI 7.4 × 10⁻⁴to 4.8 × 10⁻³ S/cm A1-5 Li₂CO₃ + (CH₂OCO₂Li)₂ S-PSf 8.7 × 10⁻⁴ to 3.6 ×10⁻³ S/cm B1 LiF + LiOH + Li₂C₂O₄ S-PSf 8.7 × 10⁻⁴ to 2.1 × 10⁻³ S/cm B2LiF + HCOLi S-PPy 2.1 × 10⁻⁴ to 8.6 × 10⁻⁴ S/cm B3 LiOH S-PAT 2.7 × 10⁻⁴to 1.1 × 10⁻³ S/cm B4 Li₂CO₃ S-PEEK 6.4 × 10⁻⁴ to 3.9 × 10⁻³ S/cm B5Li₂C₂O₄ S-PSf + PEO 9.3 × 10⁻⁴ to 7.7 × 10⁻³ S/cm B6 Li₂CO₃ + LiOHS-PANi + S-PEEK 1.4 × 10⁻³ to 6.6 × 10⁻³ S/cm

Example 8: Preparation of Solid State Electrolytes ContainingLithium-Containing Inorganic Species in a Sulfonated Polymer ViaSolution or Melt Mixing

Heavily sulfonated polymers, after sulfonation, were typically dried at50° C. for 2 days prior to its use. The lithium salts were dried at thetemperature specified below: LiCF₃SO₃ at 50° C. for 2 days, LiAsF₆ usedas received, LiBF₄ at 50° C. for 2 days, LiAlCl₄ and LiPF₆ at 50° C. for1 day. All of these lithium salts and sulfonated polymers dissolveeasily in acetonitrile or water and electrolyte films were cast fromthis solvent or water.

The data in Table 2 below again demonstrates that the presently inventedsolid state electrolytes (sulfonated polymer+lithium salt) exhibitlithium ion conductivity values that are superior to those of knownsolid state electrolytes.

Perfuoroalkyl sulfonic-type conducting salts like lithiumtri-fluoromethanesulfonate (LiTf),lithiumbis(tri-fluoromethanesulfonimidate) (LiTFSI), lithiumbis(tri-fluoro methanesulfonimide) (LiBETI), and lithiumbis(fluorosulfonyl)amide (LiFSI) are found to have high solubility in sulfonated polymers,high ionic conductivity, and high electrochemical stability. Theselithium salts with large anions can easily dissociate in the sulfonatedpolymer host and set off the free lithium cations, resulting in theincrease in ionic conductivity. It may be noted that the addition of aLi salt is known to reduce the crystallinity of PEO, but significantlyincreases the glass transition temperature of PEO, thereby reducing themobility of EO segments and, hence, Li ion conductivity. Surprisingly,this problem does not occur in the sulfonated polymers.

TABLE 2 Lithium ion conductivity of various solid state electrolytecompositions. Lithium-conducting Sample Lithium-containing polymer(sulfonated No. inorganic species (Li salt) polymer) Li-ion conductivity(S/cm) C1 LiClO₄ S-PTFE (20-80%) 6.9 × 10⁻⁵ to 1.1 × 10⁻³ S/cm C2 LiClO₄S-PEEK 8.8 × 10⁻⁵ to 2.1 × 10⁻³ S/cm C3 LiClO₄ S-PSf 7.4 × 10⁻⁵ to 8.1 ×10⁻⁴ S/cm C4 LiClO₄ S-PPy 7.5 × 10⁻⁵ to 5.5 × 10⁻⁴ S/cm C5 LiPF₆ S-PEEK2.4 × 10⁻⁴ to 1.9 × 10⁻³ S/cm C6 LiBF₄ S-PEEK 2.6 × 10⁻⁴ to 1.5 × 10⁻³S/cm C7 LiBF₄ + LiCF₃SO₃ S-PSf 9.4 × 10⁻⁵ to 9.3 × 10⁻⁴ S/cm C8 LiBOB +LiNO₃ S-PSf 8.6 × 10⁻⁵ to 7.4 × 10⁻⁴ S/cm

It may be noted that the prior art all-solid-state lithium-ion batteries(LIBs) based on inorganic solid electrolyte (ISEs) suffer from theissues of poor cycle performance, resulting from an unstableelectrolyte/electrode interface during the process ofcharging/discharging. The ISEs are not compliant or conformal to theshape or dimensional changes of an electrode, leading to poorinterfacial contact. In addition, the high rigidity of ISEs leads topoor conformability, which limits their applications in flexibledevices. The presently invented sulfonated polymer based solid stateelectrolytes have essentially eliminated these problems long associatedwith ISEs and polymer-based solid-state electrolytes.

Example 9: Preparation of Solid State Electrolytes ContainingLithium-Containing Inorganic Species in a (Non-Sulfonated) LithiumIon-Conducting Polymer Via Solution or Melt Mixing

Another group of presently invented solid state electrolytes ischaracterized by being composed of (a) a conventional electrolytepolymer (e.g. PEO, PPO, etc.) or its mixtures with a sulfonated polymerand (b) lithium-containing species (e.g. those produced by the presentlyinvented electrochemically induced electrolyte decomposition) that arenot normally used as a lithium salt in a conventional lithium-ionbattery. As indicated in Table 3 below, these solid state electrolytesalso demonstrate outstanding lithium ion conductivity values.Furthermore, As shown in FIG. 4, the lithium ion conductivity values ofa polymer mixture containing a conventional solid electrolyte polymer(PEO or PPO) and a sulfonated polymer exhibit unexpected synergisticeffect.

Not to be bound by the theory, but the presence of a different polymerand some lithium-containing inorganic species appear to be capable offorming more amorphous phase in an otherwise crystalline polymer andenabling faster or easier transport of lithium ions through theseamorphous zones.

TABLE 3 Lithium ion conductivity of various solid state electrolytecompositions. Lithium-conducting Sample Lithium-containing polymer (non-No. inorganic species sulfonated polymer) Li-ion conductivity (S/cm) D1Li₂CO₃ + (CH₂OCO₂Li)₂ PEO (15-85% by wt.) 1.4 × 10⁻⁴ to 8.7 × 10⁻⁴ S/cmD2 LiF + LiOH + Li₂C₂O₄ PEO (5-95% by wt.) 2.7 × 10⁻⁴ to 9.3 × 10⁻⁴ S/cmD3 LiF + HCOLi PEO 2.7 × 10⁻⁴ to 9.3 × 10⁻⁴ S/cm D4 Li₂CO₃ PAN 8.4 ×10⁻⁵ to 6.9 × 10⁻⁴ S/cm D5 LiOH + Li₂CO₃ PPO 8.7 × 10⁻⁵ to 6.6 × 10⁻⁴S/cm D6 LiOH + Li₂CO₃ PEO + S-PANi 5.5 × 10⁻⁴ to 2.9 × 10⁻³ S/cm D7LiOH + Li₂CO₃ (30% PEO + S-PEEK (PEO- See FIG. 4 salt) S-PEEK ratiovaried) D8 LiOH + Li₂CO₃ PEO + S-PSf 3.5 × 10⁻⁴ to 1.5 × 10⁻³ S/cm D9LiOH + Li₂CO₃ (30% PPO + S-PTFE (PPO- See FIG. 4 salt) S-PTFE ratiovaried)

Example 10: Preparation of MoS₂/RGO Hybrid Cathode Material for Li MetalCells and MOS₂ as a Filler Dispersed in a Carbon Matrix (GO=GrapheneOxide; RGO=Reduced Graphene Oxide)

Ultra-thin MoS₂/RGO hybrid was synthesized by a one-step solvothermalreaction of (NH₄)₂MoS₄ and hydrazine in an N, N-dimethylformamide (DMF)solution of oxidized graphene oxide (GO) at 200° C. In a typicalprocedure, 22 mg of (NH₄)₂MoS₄ was added to 10 mg of GO dispersed in 10ml of DMF. The mixture was sonicated at room temperature forapproximately 10 min until a clear and homogeneous solution wasobtained. After that, 0.1 ml of N₂H₄—H₂O was added. The reactionsolution was further sonicated for 30 min before being transferred to a40 mL Teflon-lined autoclave. The system was heated in an oven at 200°C. for 10 h. Product was collected by centrifugation at 8000 rpm for 5min, washed with DI water and recollected by centrifugation. The washingstep was repeated for at least 5 times to ensure that most DMF wasremoved. Finally, product was dried and made into a cathode.

Three Li metal cells using this same cathode but three differentelectrolytes were investigated. These electrolytes include the presentlyinvented solid electrolyte (C5 in Table 2), liquid electrolyte (1 M ofLiPF₆ in PC-EC solvent mixture), and a prior art PEO-LiPF₆ polymerelectrolyte. The Ragone plots (power density vs. energy density) ofthese 3 cells tested in different discharge rates (different currentdensities) are shown in FIG. 5. These data demonstrate that the Li metalsecondary cell featuring the inventive solid-state electrolyte is asgood as the cell using a liquid electrolyte, even at a high rate (highpower density). This implies that lithium transport in the presentlyinvented solid electrolyte is relatively fast. Further, compared to theliquid electrolyte-based cell that is subject to dendrite formation,flammability, and explosion issues, the battery cell featuring a solidstate electrolyte is safe.

In further contrast, the cell based on the prior art PEO polymerelectrolyte exhibits both lower energy density and power density,indicating slower lithium ion responses in this electrolyte system,given same battery components.

Example 11: Li-Ion Cells Having a Graphite Anode and Lithium IronPhosphate Cathode

Two Li-ion secondary cells using an invented solid state electrolyte (B6in Table 1) and a conventional PEO-based polymer electrolyte wereinvestigated. As shown in FIG. 6, the capacity of the inventive cellperforms relatively well even at relatively high C rates (1 C=fulldischarge in 1 hour; 10 C rate=full discharge in 1/10 hours; 0.5 Crate=full discharge in 1/0.5=2 hours, etc.). By contrast, PEO basedelectrolyte does not enable lithium ions to move fast, resulting inlower capacity.

Example 12: Preparation of Graphene-Enabled Li_(x)V₃O₈ Nano-Sheets fromV₂O₅ and LiOH as a Cathode for Li-Ion Cells

All chemicals used in this study were analytical grade and were used asreceived without further purification. V₂O₅ (99.6%, Alfa Aesar) and LiOH(99+%, Sigma-Aldrich) were used to prepare the precursor solution.Graphene oxide (GO, 1% w/v obtained in Example 2 above) was used as astructure modifier. First, V₂O₅ and LiOH in a stoichiometric V/Li ratioof 1:3 were dissolved in actively stirred de-ionized water at 50° C.until an aqueous solution of Li_(x)V₃O₈ was formed. Then, GO suspensionwas added while stirring, and the resulting suspension was atomized anddried in an oven at 160° C. to produce the spherical compositeparticulates of GO/Li_(x)V₃O₈ nano-sheets and the sample was designatedNLVO-1. Corresponding Li_(x)V₃O₈ materials were obtained undercomparable processing conditions, but without graphene oxide sheets. Thesample was designated as LVO-2.

The Nyquist plots obtained from electrical impedance tests show asemicircle in the high to medium frequency range, which describes thecharge-transfer resistance for both electrodes. The intercept value isconsidered to represent the total electrical resistance offered by theelectrolyte. The inclined line represents the Warburg impedance at lowfrequency, which indicates the diffusion of ions in the solid matrix.The values of Rct for the vanadium oxide alone and graphene-enhancedcomposite electrodes are about 50.0 and 350.0Ω for NLVO-1 and LVO-2,respectively. The Rct of the composite electrode is much smaller thanthat of the LVO electrode. Therefore, the presence of graphene (<2% byweight in this case) in the vanadium oxide composite has dramaticallyreduced the internal charge transfer resistance and improved the batteryperformance upon extended cycling.

An additional set of graphene-enabled Li_(x)V₃O₈ nano-sheet compositeparticulates was produced from V₂O₅ and LiOH under comparableconditions, but was dried under different atomization temperatures,pressures, and gas flow rates to achieve four samples of compositeparticulates with four different Li_(x)V₃O₈ nano-sheet averagethicknesses (4.6 nm, 8.5 nm, 14 nm, and 35 nm). A sample of Li_(x)V₃O₈sheets/rods with an average thickness/diameter of 76 nm was alsoobtained without the presence of graphene oxide sheets (but, with thepresence of carbon black particles) under the same processing conditionsfor the graphene-enhanced particulates with a nano-sheet averagethickness of 35 nm. It seems that carbon black is not as good anucleating agent as graphene for the formation of Li_(x)V₃O₈ nano-sheetcrystals. The specific capacity of these cathode materials wasinvestigated using Li foil or a layer of natural graphite particles asan anode for a lithium metal rechargeable battery or lithium-ionbattery, respectively. For comparison purposes, both a presentlyinvented solid state electrolyte and a conventional liquid electrolytewere incorporated as the electrolyte for these cells. Theelectrochemical testing results also indicate that both electrolyteslead to comparable energy densities at very high discharge rates, butthe solid state electrolyte leads to better energy densities at lowrates. This observation is surprising since lithium ions are normallyconsidered to move faster in a liquid electrolyte than in a solidelectrolyte, which is presumably more conducive to efficient use of theelectrode active material. Most significantly, there is no dendriteissue in solid electrolyte based cells even when the batteries werecharged and discharged in a fast rate and no fire/flame when the cellswere over-charged.

Example 13: Electrochemical Deposition of S on Various Webs or Paper asa Cathode Active Material for Li—S Batteries

The electrochemical deposition of sulfur (S) was conducted before thecathode active layer was incorporated into a lithium-sulfur battery cell(Li—S). The anode, the electrolyte, and the integral layer of porousgraphene structure (serving as a cathode layer) are positioned in anexternal container outside of a lithium-sulfur cell. The neededapparatus is similar to an electro-plating system, which is well-knownin the art.

In a typical procedure, a metal polysulfide (Li₂S₉ and Nai₂S₆) isdissolved in a solvent (e.g. mixture of DOL/DME at a volume ratio from1:3 to 3:1) to form an electrolyte solution. The electrolyte solution isthen poured into a chamber or reactor under a dry and controlledatmosphere condition (e.g. He or Nitrogen gas). A metal foil was used asthe anode and a layer of the porous graphene structure as the cathode;both being immersed in the electrolyte solution. This configurationconstitutes an electrochemical deposition system. The step ofelectrochemically depositing nano-scaled sulfur particles or coating onthe graphene surfaces was conducted at a current density preferably inthe range of 1 mA/g to 10 A/g, based on the layer weight of the porousgraphene structure.

The chemical reactions that occurred in this reactor may be representedby the following equation: M_(x)S_(y)→M_(x)S_(y-z)+zS (typically z=1-4).Quite surprisingly, the precipitated S is preferentially nucleated andgrown on massive graphene surfaces to form nano-scaled coating or nanoparticles. The coating thickness or particle diameter and the amount ofS coating/particles was controlled by the specific surface area,electro-chemical reaction current density, temperature and time. Ingeneral, a lower current density and lower reaction temperature lead toa more uniform distribution of S and the reactions are easier tocontrol. A longer reaction time leads to a larger amount of S depositedon graphene surfaces and the reaction is ceased when the sulfur sourceis consumed or when a desired amount of S is deposited.

The specific discharge capacities of two Li—S cells (one containing thepresently invented solid state electrolyte and one containing prior artliquid electrolyte) were plotted as a function of the number of cycles(FIG. 8). The Ragone plots of the two cells, plus one cell containing aconventional PEO-based polymer solid electrolyte, are shown in FIG. 7.Quite unexpectedly, the cells containing the presently invented solidstate electrolyte actually show the highest energy densities among thethree ells, and a more stable cycling behavior even though all threecells have otherwise identical configurations. It appears that theinvented solid state electrolyte not only serves to stop dendritepenetration, but also prevent sulfur and lithium polysulfide speciesfrom being dissolved in the liquid electrolyte and migrated from thecathode toward the anode side. Such a blocking action prevents thelithium polysulfide from reaching and reacting with the Li metal at theanode, which otherwise would form Li₂S that irreversibly deposits on Limetal surface. This so-called shuttling effect in all Li—S cells isactually eliminated due to the presence of this solid state electrolyte.This is an un-intended, but highly beneficial result.

We have achieved a specific energy>500 Wh/kg in many Li—S cells (someeven >600 wh/kg) and none of these cells have any dendrite issue.

Example 14: Li-Air Cells with Ionic Liquid Electrolytes

To test the performance of the Li-air batteries employing a solid stateelectrolyte and those with a liquid electrolyte, several pouch cellswith dimension of 5 cm×5 cm were built. Porous carbon electrodes wereprepared by first preparing ink slurries by dissolving a 90 wt. %EC600JD Ketjen black (AkzoNobel) and 5 wt. % Kynar PVDF (ArkemaCorporation) in Nmethyl-2-pyrrolidone (NMP). Air electrodes wereprepared with a carbon loading of approximately 20.0 mg/cm² byhand-painting the inks onto a carbon cloth (PANEX 35, ZoltekCorporation), which was then dried at 180° C. overnight. The totalgeometric area of the electrodes was 3.93 cm². The Li/O₂ test pouchcells were assembled in an argon-filled glove box. Each cell consists ofmetallic lithium anode and the air electrode as a cathode, prepared asmentioned above. A copper current collector for the anode and analuminum current collector for the cathode were used. In one Li/O₂ cell,a layer of LiTFSI/S-PEEK solid state electrolyte was implemented betweenthe anode layer (Li foil) and the cathode layer. The cathode was soakedin the oxygen saturated EMITFSI-DOL/LiTFSI solution for 24 hours and wasplaced under vacuum for an hour before being included in the cellassembly. For comparison, a Celgard 3401 separator separating the twoelectrodes was soaked in 1 M LiTFSI-DOL/EMITFSI (6/4) solutions for aminimum of 24 hours.

The cells were placed in an oxygen-filled glove box where oxygenpressure was maintained at 1 atm. Cell charge-discharge was carried outwith a battery cycler at the current rate of 0.1 mA/cm² at roomtemperature. It was found surprisingly that a Li-air featuring the solidstate electrolyte exhibits a higher round-trip efficiency for cells(75%) as compared with their counterparts with a liquid electrolyte(64%). Most significantly, the cells containing liquid electrolytetended to fail in 25-35 charge-discharge cycles. In contrast, thepresently invented cells containing a solid state electrolyte usuallylasted for more than 100 cycles without experiencing anydendrite-induced failure.

Examples 15: Evaluation of Electrochemical Performance of Various LiSecondary Batteries

A broad array of Li metal secondary (rechargeable) batteries wasinvestigated. None of the batteries containing a solid state electrolyteprepared according to instant invention were found to fail due todendrite penetration through the separator layer, as usually observedwith lithium metal batteries containing liquid electrolyte, based on theobservation of post-testing inspection on a large number of batterycells.

Li ion storage capacities of many cells were measured periodically andrecorded as a function of the number of cycles. The specific dischargecapacity herein referred to is the total charge inserted into thecathode during the discharge, per unit mass of the composite cathode(counting the weights of cathode active material, conductive additive orsupport, binder, and any optional additive combined). The specificcharge capacity refers to the amount of charges per unit mass of thecomposite cathode. The specific energy and specific power valuespresented in this section are based on the total cell weight. Themorphological or micro-structural changes of selected samples after adesired number of repeated charging and recharging cycles were observedusing both transmission electron microscopy (TEM) and scanning electronmicroscopy (SEM). The presently invented dendrite-intercepting layerenables the safe operation of many lithium metal and sodium metalsecondary batteries capable of storing an energy density of 300-400Wh/kg (e.g. lithium metal-metal oxide cells), 400-750 Wh/kg (e.g. Li—Scells), and >1,000 Wh/kg (e.g. Li-air cells) for a long cycle lifewithout a dendrite penetration problem.

In summary, the present invention provides an innovative, versatile, andsurprisingly effective platform materials technology that enables thedesign and manufacture of superior and safe alkali metal rechargeablebatteries that feature a solid state electrolyte having a high lithiumtransport rate. The lithium dendrite issue in these high energy and highpower cells is essentially eliminated, making it possible for thesebatteries to be widely implemented for electric vehicle, renewableenergy storage, and electronic device applications.

1. A solid state electrolyte composition for a rechargeable lithiumbattery, said electrolyte composition comprising a lithiumion-conducting polymer matrix or binder and lithium ion-conductinginorganic species that is dispersed in or chemically bonded by saidpolymer matrix or binder, wherein said lithium ion-conducting inorganicspecies is selected from Li₂CO₃, Li₂O, Li₂C₂O₄, LiOH, LiX, ROCO₂Li,HCOLi, ROLi, (ROCO₂Li)₂, (CH₂OCO₂Li)₂, Li₂S, Li_(x)SO_(y), or acombination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group,x=0-1, y=1-4; and wherein the polymer matrix or binder is in an amountfrom 1% to 99% by volume of the electrolyte composition.
 2. The solidstate electrolyte composition of claim 1, wherein said polymer matrix orbinder comprises a sulfonated polymer, a mixture of a sulfonated polymerand an electron-conducting polymer, a mixture of a sulfonated polymerand an electronically non-conducting polymer, or a mixture of anelectron-conducting polymer and a lithium ion-conducting polymer.
 3. Thesolid state electrolyte composition of claim 1, wherein said polymermatrix or binder is selected from sulfonated polyaniline, sulfonatedpolypyrrole, sulfonated polythiophene, sulfonated polyfuran, or acombination thereof.
 4. A solid state electrolyte composition for arechargeable lithium battery, said electrolyte composition comprising alithium ion-conducting polymer matrix or binder selected from asulfonated polymer and a lithium ion-conducting inorganic species thatis dispersed in or chemically bonded by said polymer matrix or binder,wherein said lithium ion-conducting inorganic species contains a lithiumsalt selected from lithium perchlorate, LiClO₄, lithiumhexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄, lithiumhexafluoroarsenide, LiAsF₆, lithium trifluoro-metasulfonate, LiCF₃SO₃,bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂, lithiumbis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate, LiBF₂C₂O₄,lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate, LiNO₃,Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof; and wherein the polymer matrixor binder is in an amount from 1% to 99% by volume of the electrolytecomposition.
 5. The solid state electrolyte composition of claim 2,wherein said sulfonated polymer is selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene, sulfonated perfluoroethylene-propylenecopolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer,sulfonated polyvinylidenefluoride, sulfonated copolymers ofpolyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof.
 6. The solid state electrolyte composition of claim 4, whereinsaid sulfonated polymer is selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene, sulfonated perfluoroethylene-propylenecopolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer,sulfonated polyvinylidenefluoride, sulfonated copolymers ofpolyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof
 7. The solid state electrolyte composition of claim 1, whereinsaid polymer matrix or binder comprises a mixture of anelectron-conducting polymer and a lithium ion-conducting polymer; saidlithium ion-conducting polymer is selected from the group consisting ofpoly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene,sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene,sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide,sulfonated styrene-butadiene copolymers, sulfonated polychloro-trifluoroethylene, sulfonated perfluoroethylene-propylenecopolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer,sulfonated polyvinylidenefluoride, sulfonated copolymers ofpolyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene,sulfonated copolymers of ethylene and tetrafluoroethylene,polybenzimidazole, and chemical derivatives, copolymers, and blendsthereof, wherein the electron-conducting polymer-to-lithiumion-conducting polymer weight ratio is from 1/99 to 99/1.
 8. The solidstate electrolyte composition of claim 1, wherein said polymer matrix orbinder comprises a mixture of a lithium ion-conducting polymer and anelectron-conducting polymer and wherein said electron-conducting polymeris selected from the group consisting of polyaniline, polypyrrole,polythiophene, polyfuran, bi-cyclic polymers, derivatives thereof, andcombinations thereof.
 9. The solid state electrolyte composition ofclaim 1, wherein said polymer matrix or binder contains a lithiumion-conducting polymer selected from poly(ethylene oxide) (PEO),Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methylmethacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), aderivative thereof, or a combination thereof, or a mixture thereof witha sulfonated polymer.
 10. The solid state electrolyte composition ofclaim 1, wherein said polymer matrix further contains particles of afiller dispersed therein.
 11. The solid state electrolyte composition ofclaim 8, wherein said filler is selected from a metal oxide, metalcarbide, metal nitride, metal boride, metal dichalcogenide, or acombination thereof.
 12. The solid state electrolyte composition ofclaim 8, wherein said filler is selected from an oxide, dichalcogenide,trichalcogenide, sulfide, selenide, or telluride of niobium, zirconium,molybdenum, hafnium, tantalum, tungsten, titanium, vanadium, chromium,cobalt, manganese, iron, or nickel in a nanowire, nano-disc,nano-ribbon, or nano platelet form.
 13. The solid state electrolytecomposition of claim 8, wherein said filler is selected from nano discs,nano platelets, or nano sheets of an inorganic material selected from:(a) bismuth selenide or bismuth telluride, (b) transition metaldichalcogenide or trichalcogenide, (c) sulfide, selenide, or tellurideof niobium, zirconium, molybdenum, hafnium, tantalum, tungsten,titanium, cobalt, manganese, iron, nickel, or a transition metal; (d)boron nitride, or (e) a combination thereof; wherein said discs,platelets, or sheets have a thickness less than 100 nm.
 14. The solidstate electrolyte composition of claim 1, wherein said lithiumion-conducting species has a room temperature ion conductivity no lessthan 10⁻⁴ S/cm.
 15. The solid state electrolyte composition of claim 1,wherein said lithium ion-conducting species has a room temperature ionconductivity no less than 10⁻³ S/cm.
 16. A lithium secondary batterycontaining an anode, a cathode, and the solid state electrolyte ofclaim
 1. 17. A lithium secondary battery containing an anode, a cathode,and the solid state electrolyte of claim
 4. 18. The lithium secondarybattery of claim 16, which is a lithium-ion battery, a rechargeablelithium metal battery, a lithium-sulfur battery, a lithium-seleniumbattery, or a lithium-air battery.
 19. The lithium secondary battery ofclaim 17, which is a lithium-ion battery, a rechargeable lithium metalbattery, a lithium-sulfur battery, a lithium-selenium battery, or alithium-air battery.
 20. A process for producing the solid stateelectrolyte composition of claim 1, said process comprising (a)preparing a working electrode containing a lithium ion-conductingpolymer; (b) preparing a counter electrode containing lithium metal oralloy; (c) bringing said working electrode and said counter electrode incontact with an electrolyte containing a solvent and a lithium saltdissolved in said solvent; and (d) applying a current or voltage to saidworking electrode and said counter electrode to induce anelectrochemical oxidative decomposition and/or a reductive decompositionof said electrolyte and/or said salt for forming said lithium-containinginorganic species that are attached or bonded to said lithiumion-conducting polymer for forming said solid state electrolytecomposition.
 21. A process for producing the solid state electrolytecomposition of claim 1, said process comprising (a) preparing a workingelectrode containing a carbon material selected from an amorphouscarbon, polymeric carbon, activated carbon, carbon black, graphiteparticles, graphene sheets, carbon nanotubes, carbon fibers, graphitefibers, carbon nano-fibers, or a combination thereof; (b) preparing acounter electrode containing lithium metal or alloy; (c) bringing saidworking electrode and said counter electrode in contact with anelectrolyte containing a solvent and a lithium salt dissolved in saidsolvent; (d) applying a current or voltage to said working electrode andsaid counter electrode to induce an electrochemical oxidativedecomposition and/or a reductive decomposition of said electrolyteand/or said salt for forming said lithium-containing inorganic speciesthat are attached to said carbon material; and (e) mixing saidlithium-containing inorganic species, with or without said carbonmaterial, with a lithium ion-conducting polymer for forming said solidstate electrolyte composition.
 22. The process of claim 20, which is aroll-to-roll process that includes preparing said working electrode in aroll form supported by a feeder roller, and said step of bringing saidworking electrode and said counter electrode in contact with saidelectrolyte contains unwinding said working electrode from said feederroller, and feeding said working electrode into said electrolyte.
 23. Aprocess for producing the solid state electrolyte composition of claim1, said process comprising (a) preparing a working electrode containinga lithium ion-conducting polymer; (b) preparing a counter electrodecontaining lithium metal or alloy; (c) bringing said working electrodeand said counter electrode in physical contact with each other and incontact with an electrolyte containing a solvent and a lithium saltdissolved in said solvent; wherein said working electrode and saidcounter electrode are brought to be at the same electrochemicalpotential level, inducing a chemical reaction between said lithium metalor alloy and said lithium ion-conducting polymer and inducingelectrochemical decomposition of said electrolyte for forming saidlithium-containing inorganic species that are attached or chemicallybonded to said lithium ion-conducting polymer to form said solid stateelectrolyte composition.
 24. A process for producing the solid stateelectrolyte composition of claim 1, said process comprising (a)preparing a working electrode containing a carbon material selected froman amorphous carbon, polymeric carbon, activated carbon, carbon black,graphite particles, graphene sheets, carbon nanotubes, carbon fibers,graphite fibers, carbon nano-fibers, or a combination thereof; (b)preparing a counter electrode containing lithium metal or alloy; (c)bringing said working electrode and said counter electrode in physicalcontact with each other and in contact with an electrolyte containing asolvent and a lithium salt dissolved in said solvent; wherein saidworking electrode and said counter electrode are brought to be at thesame electrochemical potential level, inducing a chemical reactionbetween said lithium metal or alloy and said carbon material andinducing electrochemical decomposition of said electrolyte for formingsaid lithium-containing inorganic species on surfaces of said carbonmaterial; and (d) mixing said lithium-containing inorganic species, withor without said carbon material, with a lithium ion-conducting polymerfor forming said solid state electrolyte composition.
 25. The process ofclaim 23, which is conducted in a roll-to-roll manner.
 26. The processof claim 20, wherein said lithium ion-conducting polymer contains asulfonated polymer or a mixture of a sulfonated polymer and a polymerselected from poly(ethylene oxide) (PEO), Polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), aderivative thereof, or a combination thereof.
 27. The process of claim23, wherein said lithium ion-conducting polymer contains a sulfonatedpolymer or a mixture of a sulfonated polymer and a polymer selected frompoly(ethylene oxide) (PEO), Polypropylene oxide (PPO),poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA),poly(vinylidene fluoride) (PVdF), Poly bis-methoxyethoxyethoxide-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane,and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), aderivative thereof, or a combination thereof.
 28. The process of claim20, wherein said lithium salt is selected from lithium perchlorate,LiClO₄, lithium hexafluorophosphate, LiPF₆, lithium borofluoride, LiBF₄,lithium hexafluoroarsenide, LiAsF₆, lithium trifluoro-metasulfonate,LiCF₃SO₃, bis-trifluoromethyl sulfonylimide lithium, LiN(CF₃SO₂)₂,lithium bis(oxalato)borate, LiBOB, lithium oxalyldifluoroborate,LiBF₂C₂O₄, lithium oxalyldifluoroborate, LiBF₂C₂O₄, lithium nitrate,LiNO₃, Li-Fluoroalkyl-Phosphates, LiPF₃(CF₂CF₃)₃, lithiumbisperfluoro-ethysulfonylimide, LiBETI, lithiumbis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide,lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-basedlithium salt, or a combination thereof.
 29. The process of claim 20,wherein said solvent is selected from 1,3-dioxolane (DOL),1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether (TEGDME),poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutylether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylenecarbonate (EC), dimethyl carbonate (DMC), methylethyl carbonate (MEC),diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylenecarbonate (PC), gamma-butyrolactone (γ-BL), acetonitrile (AN), ethylacetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene,methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate(VC), allyl ethyl carbonate (AEC), a hydrofluoroether, an ionic liquidsolvent, or a combination thereof.
 30. A process for producing the solidstate electrolyte composition of claim 1, said process includes anoperation of solution mixing, melt mixing, in situ precipitation ofinorganic species in a lithium ion-conducting polymer, physical orchemical vapor deposition, electrochemical deposition of said inorganicspecies on surfaces of a carbon material, electrochemical deposition ofsaid inorganic species on surfaces of a lithium ion-conducting material,or a combination thereof.